[SCM-318] Allow tags to be removed with Git implementation

This closes #79
diff --git a/maven-scm-api/src/main/java/org/apache/maven/scm/command/tag/AbstractTagCommand.java b/maven-scm-api/src/main/java/org/apache/maven/scm/command/tag/AbstractTagCommand.java
index 41493d2..c0b4d56 100644
--- a/maven-scm-api/src/main/java/org/apache/maven/scm/command/tag/AbstractTagCommand.java
+++ b/maven-scm-api/src/main/java/org/apache/maven/scm/command/tag/AbstractTagCommand.java
@@ -37,7 +37,7 @@
     extends AbstractCommand
 {
     /**
-     * @deprecated use method {@link #executeTagCommand(ScmProviderRepository, ScmFileSet, String, ScmTagParameters)} 
+     * @deprecated use method {@link #executeTagCommand(ScmProviderRepository, ScmFileSet, String, ScmTagParameters)}
      * @param repository
      * @param fileSet
      * @param tagName
@@ -54,8 +54,8 @@
 
     protected abstract ScmResult executeTagCommand( ScmProviderRepository repository, ScmFileSet fileSet,
                                                     String tagName, ScmTagParameters scmTagParameters )
-        throws ScmException;    
-    
+        throws ScmException;
+
     /** {@inheritDoc} */
     public ScmResult executeCommand( ScmProviderRepository repository, ScmFileSet fileSet,
                                      CommandParameters parameters )
@@ -81,5 +81,5 @@
 
         return executeTagCommand( repository, fileSet, tagName, scmTagParameters );
     }
-    
+
 }
diff --git a/maven-scm-api/src/main/java/org/apache/maven/scm/command/untag/AbstractUntagCommand.java b/maven-scm-api/src/main/java/org/apache/maven/scm/command/untag/AbstractUntagCommand.java
new file mode 100644
index 0000000..bbbb0c8
--- /dev/null
+++ b/maven-scm-api/src/main/java/org/apache/maven/scm/command/untag/AbstractUntagCommand.java
@@ -0,0 +1,48 @@
+package org.apache.maven.scm.command.untag;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import org.apache.maven.scm.CommandParameter;
+import org.apache.maven.scm.CommandParameters;
+import org.apache.maven.scm.ScmException;
+import org.apache.maven.scm.ScmFileSet;
+import org.apache.maven.scm.ScmResult;
+import org.apache.maven.scm.command.AbstractCommand;
+import org.apache.maven.scm.provider.ScmProviderRepository;
+
+/** {@inheritDoc} */
+public abstract class AbstractUntagCommand
+    extends AbstractCommand
+{
+    protected abstract ScmResult executeUntagCommand( ScmProviderRepository repository,
+        ScmFileSet fileSet, String tagName )
+        throws ScmException;
+
+    /** {@inheritDoc} */
+    public ScmResult executeCommand( ScmProviderRepository repository, ScmFileSet fileSet,
+                                     CommandParameters parameters )
+        throws ScmException
+    {
+        String tagName = parameters.getString( CommandParameter.TAG_NAME );
+
+        return executeUntagCommand( repository, fileSet, tagName );
+    }
+
+}
diff --git a/maven-scm-api/src/main/java/org/apache/maven/scm/command/untag/UntagScmResult.java b/maven-scm-api/src/main/java/org/apache/maven/scm/command/untag/UntagScmResult.java
new file mode 100644
index 0000000..47babaf
--- /dev/null
+++ b/maven-scm-api/src/main/java/org/apache/maven/scm/command/untag/UntagScmResult.java
@@ -0,0 +1,44 @@
+package org.apache.maven.scm.command.untag;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import org.apache.maven.scm.ScmResult;
+
+/** {@inheritDoc} */
+public class UntagScmResult
+    extends ScmResult
+{
+    private static final long serialVersionUID = -5068975000282095635L;
+
+    public UntagScmResult( String commandLine, String providerMessage, String commandOutput, boolean success )
+    {
+        super( commandLine, providerMessage, commandOutput, success );
+    }
+
+    public UntagScmResult( String commandLine )
+    {
+        super( commandLine, null, null, true );
+    }
+
+    public UntagScmResult( ScmResult result )
+    {
+        super( result );
+    }
+}
diff --git a/maven-scm-api/src/main/java/org/apache/maven/scm/provider/AbstractScmProvider.java b/maven-scm-api/src/main/java/org/apache/maven/scm/provider/AbstractScmProvider.java
index dfcc88d..dcacd11 100644
--- a/maven-scm-api/src/main/java/org/apache/maven/scm/provider/AbstractScmProvider.java
+++ b/maven-scm-api/src/main/java/org/apache/maven/scm/provider/AbstractScmProvider.java
@@ -49,6 +49,7 @@
 import org.apache.maven.scm.command.status.StatusScmResult;
 import org.apache.maven.scm.command.tag.TagScmResult;
 import org.apache.maven.scm.command.unedit.UnEditScmResult;
+import org.apache.maven.scm.command.untag.UntagScmResult;
 import org.apache.maven.scm.command.update.UpdateScmResult;
 import org.apache.maven.scm.log.ScmLogDispatcher;
 import org.apache.maven.scm.log.ScmLogger;
@@ -901,6 +902,17 @@
 
     /**
      * {@inheritDoc}
+     */
+    public UntagScmResult untag( ScmRepository repository, ScmFileSet fileSet,
+        CommandParameters parameters )
+        throws ScmException
+    {
+        getLogger().warn( "Provider " + this.getScmType() + " does not support untag operation." );
+        return new UntagScmResult( "", null, null, true );
+    }
+
+    /**
+     * {@inheritDoc}
      *
      * @deprecated
      */
diff --git a/maven-scm-api/src/main/java/org/apache/maven/scm/provider/ScmProvider.java b/maven-scm-api/src/main/java/org/apache/maven/scm/provider/ScmProvider.java
index a2d005f..168c846 100644
--- a/maven-scm-api/src/main/java/org/apache/maven/scm/provider/ScmProvider.java
+++ b/maven-scm-api/src/main/java/org/apache/maven/scm/provider/ScmProvider.java
@@ -45,6 +45,7 @@
 import org.apache.maven.scm.command.status.StatusScmResult;
 import org.apache.maven.scm.command.tag.TagScmResult;
 import org.apache.maven.scm.command.unedit.UnEditScmResult;
+import org.apache.maven.scm.command.untag.UntagScmResult;
 import org.apache.maven.scm.command.update.UpdateScmResult;
 import org.apache.maven.scm.log.ScmLogger;
 import org.apache.maven.scm.repository.ScmRepository;
@@ -642,6 +643,18 @@
         throws ScmException;
 
     /**
+     * Deletes a tag.
+     *
+     * @param repository the source control system
+     * @param fileSet    a fileset with the relevant working directory as basedir
+     * @param parameters
+     * @return
+     * @throws ScmException if any
+     */
+    UntagScmResult untag( ScmRepository repository, ScmFileSet fileSet, CommandParameters parameters )
+        throws ScmException;
+
+    /**
      * Tag (or label in some systems) will tag the source file with a certain tag
      *
      * @param repository the source control system
diff --git a/maven-scm-plugin/pom.xml b/maven-scm-plugin/pom.xml
index 9df467a..f865c36 100644
--- a/maven-scm-plugin/pom.xml
+++ b/maven-scm-plugin/pom.xml
@@ -128,6 +128,11 @@
       <artifactId>maven-scm-provider-svntest</artifactId>
       <scope>test</scope>
     </dependency>
+      <dependency>
+          <groupId>org.apache.maven.scm</groupId>
+          <artifactId>maven-scm-provider-gittest</artifactId>
+          <scope>test</scope>
+      </dependency>
   </dependencies>
 
   <build>
diff --git a/maven-scm-plugin/src/main/java/org/apache/maven/scm/plugin/UntagMojo.java b/maven-scm-plugin/src/main/java/org/apache/maven/scm/plugin/UntagMojo.java
new file mode 100644
index 0000000..3368b53
--- /dev/null
+++ b/maven-scm-plugin/src/main/java/org/apache/maven/scm/plugin/UntagMojo.java
@@ -0,0 +1,76 @@
+package org.apache.maven.scm.plugin;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import java.io.IOException;
+import org.apache.maven.plugin.MojoExecutionException;
+import org.apache.maven.plugins.annotations.Mojo;
+import org.apache.maven.plugins.annotations.Parameter;
+import org.apache.maven.scm.CommandParameter;
+import org.apache.maven.scm.CommandParameters;
+import org.apache.maven.scm.ScmException;
+import org.apache.maven.scm.command.untag.UntagScmResult;
+import org.apache.maven.scm.provider.ScmProvider;
+import org.apache.maven.scm.repository.ScmRepository;
+
+/**
+ * Untag the project.
+ */
+@Mojo( name = "untag", aggregator = true )
+public class UntagMojo
+    extends AbstractScmMojo
+{
+    /**
+     * The tag name.
+     */
+    @Parameter( property = "tag", required = true )
+    private String tag;
+
+    /** {@inheritDoc} */
+    public void execute()
+        throws MojoExecutionException
+    {
+        super.execute();
+
+        try
+        {
+            ScmRepository repository = getScmRepository();
+            ScmProvider provider = getScmManager().getProviderByRepository( repository );
+
+            String finalTag = provider.sanitizeTagName( tag );
+            getLog().info( "Final Tag Name: '" + finalTag + "'" );
+
+            CommandParameters parameters = new CommandParameters();
+            parameters.setString( CommandParameter.TAG_NAME, finalTag );
+
+            UntagScmResult result = provider.untag( repository, getFileSet(), parameters );
+
+            checkResult( result );
+        }
+        catch ( IOException e )
+        {
+            throw new MojoExecutionException( "Cannot run untag command", e );
+        }
+        catch ( ScmException e )
+        {
+            throw new MojoExecutionException( "Cannot run untag command", e );
+        }
+    }
+}
diff --git a/maven-scm-plugin/src/test/java/org/apache/maven/scm/plugin/UntagMojoTest.java b/maven-scm-plugin/src/test/java/org/apache/maven/scm/plugin/UntagMojoTest.java
new file mode 100644
index 0000000..07ac9ed
--- /dev/null
+++ b/maven-scm-plugin/src/test/java/org/apache/maven/scm/plugin/UntagMojoTest.java
@@ -0,0 +1,116 @@
+package org.apache.maven.scm.plugin;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import java.io.File;
+
+import org.apache.maven.plugin.MojoExecutionException;
+import org.apache.maven.plugin.testing.AbstractMojoTestCase;
+import org.apache.maven.scm.provider.git.GitScmTestUtils;
+import org.codehaus.plexus.util.FileUtils;
+import org.codehaus.plexus.util.StringUtils;
+
+public class UntagMojoTest
+    extends AbstractMojoTestCase
+{
+    File checkoutDir;
+
+    File repository;
+
+    protected void setUp()
+        throws Exception
+    {
+        super.setUp();
+
+        checkoutDir = getTestFile( "target/checkout" );
+
+        repository = getTestFile( "target/repository" );
+
+
+        GitScmTestUtils.initRepo( "src/test/resources/git", repository, checkoutDir );
+
+        CheckoutMojo checkoutMojo = (CheckoutMojo) lookupMojo( "checkout", getTestFile(
+            "src/test/resources/mojos/untag/checkout.xml" ) );
+        checkoutMojo.setWorkingDirectory( checkoutDir );
+
+        String connectionUrl = checkoutMojo.getConnectionUrl();
+        connectionUrl = StringUtils.replace( connectionUrl, "${basedir}", getBasedir() );
+        connectionUrl = StringUtils.replace( connectionUrl, "\\", "/" );
+        checkoutMojo.setConnectionUrl( connectionUrl );
+
+        checkoutMojo.setCheckoutDirectory( checkoutDir );
+
+        checkoutMojo.execute();
+
+        // Add a default user to the config
+        GitScmTestUtils.setDefaultUser( checkoutDir );
+    }
+
+    public void testUntag()
+        throws Exception
+    {
+        TagMojo tagMojo = (TagMojo) lookupMojo( "tag", getTestFile( "src/test/resources/mojos/untag/tag.xml" ) );
+        tagMojo.setWorkingDirectory( checkoutDir );
+        tagMojo.setConnectionUrl( getConnectionLocalAddress( tagMojo ) );
+        tagMojo.execute();
+
+        CheckoutMojo checkoutMojo =
+            (CheckoutMojo) lookupMojo( "checkout", getTestFile( "src/test/resources/mojos/untag/checkout-tag.xml" ) );
+        checkoutMojo.setWorkingDirectory( new File( getBasedir() ) );
+        checkoutMojo.setConnectionUrl( getConnectionLocalAddress( checkoutMojo ) );
+
+        File tagCheckoutDir = getTestFile( "target/tags/mytag" );
+
+        if ( tagCheckoutDir.exists() )
+        {
+            FileUtils.deleteDirectory( tagCheckoutDir );
+        }
+
+        checkoutMojo.setCheckoutDirectory( tagCheckoutDir );
+        checkoutMojo.execute();
+
+        UntagMojo mojo = (UntagMojo) lookupMojo( "untag", getTestFile( "src/test/resources/mojos/untag/untag.xml" ) );
+        mojo.setWorkingDirectory( checkoutDir );
+        mojo.setConnectionUrl( getConnectionLocalAddress( mojo ) );
+
+        mojo.execute();
+
+        FileUtils.deleteDirectory( tagCheckoutDir );
+
+        try
+        {
+            checkoutMojo.execute();
+
+            fail( "mojo execution must fail." );
+        }
+        catch ( MojoExecutionException e )
+        {
+            assertTrue( true );
+        }
+    }
+
+    private String getConnectionLocalAddress( AbstractScmMojo mojo )
+    {
+        String connectionUrl = mojo.getConnectionUrl();
+        connectionUrl = StringUtils.replace( connectionUrl, "${basedir}", getBasedir() );
+        connectionUrl = StringUtils.replace( connectionUrl, "\\", "/" );
+        return connectionUrl;
+    }
+}
diff --git a/maven-scm-plugin/src/test/resources/git/.gitattributes b/maven-scm-plugin/src/test/resources/git/.gitattributes
new file mode 100644
index 0000000..5e0feff
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/.gitattributes
@@ -0,0 +1,3 @@
+objects/** binary
+* text eol=lf
+
diff --git a/maven-scm-plugin/src/test/resources/git/HEAD b/maven-scm-plugin/src/test/resources/git/HEAD
new file mode 100644
index 0000000..cb089cd
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/HEAD
@@ -0,0 +1 @@
+ref: refs/heads/master
diff --git a/maven-scm-plugin/src/test/resources/git/config b/maven-scm-plugin/src/test/resources/git/config
new file mode 100644
index 0000000..c53d818
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/config
@@ -0,0 +1,5 @@
+[core]
+	repositoryformatversion = 0
+	filemode = true
+	bare = true
+	ignorecase = true
diff --git a/maven-scm-plugin/src/test/resources/git/description b/maven-scm-plugin/src/test/resources/git/description
new file mode 100644
index 0000000..c6f25e8
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/description
@@ -0,0 +1 @@
+Unnamed repository; edit this file to name it for gitweb.
diff --git a/maven-scm-plugin/src/test/resources/git/hooks/empty.txt b/maven-scm-plugin/src/test/resources/git/hooks/empty.txt
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/hooks/empty.txt
diff --git a/maven-scm-plugin/src/test/resources/git/info/exclude b/maven-scm-plugin/src/test/resources/git/info/exclude
new file mode 100644
index 0000000..2c87b72
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/info/exclude
@@ -0,0 +1,6 @@
+# git-ls-files --others --exclude-from=.git/info/exclude
+# Lines that start with '#' are comments.
+# For a project mostly in C, the following would be a good set of
+# exclude patterns (uncomment them if you want to use them):
+# *.[oa]
+# *~
diff --git a/maven-scm-plugin/src/test/resources/git/logs/HEAD b/maven-scm-plugin/src/test/resources/git/logs/HEAD
new file mode 100644
index 0000000..3cf80ca
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/logs/HEAD
@@ -0,0 +1,3 @@
+0000000000000000000000000000000000000000 c51dcd33e7b71897603c203b5e0afc1d75f70051 Mark Struberg <struberg@yahoo.de> 1196106917 +0100
+c51dcd33e7b71897603c203b5e0afc1d75f70051 baa229a9193371fad604444f64c4f26f8ff702f3 Mark Struberg <struberg@yahoo.de> 1197041894 +0100	push
+baa229a9193371fad604444f64c4f26f8ff702f3 1d308c3b92eb0df9c0dc76436d50edfd0ca41d18 Mark Struberg <struberg@yahoo.de> 1197042012 +0100	push
diff --git a/maven-scm-plugin/src/test/resources/git/logs/refs/heads/master b/maven-scm-plugin/src/test/resources/git/logs/refs/heads/master
new file mode 100644
index 0000000..3cf80ca
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/logs/refs/heads/master
@@ -0,0 +1,3 @@
+0000000000000000000000000000000000000000 c51dcd33e7b71897603c203b5e0afc1d75f70051 Mark Struberg <struberg@yahoo.de> 1196106917 +0100
+c51dcd33e7b71897603c203b5e0afc1d75f70051 baa229a9193371fad604444f64c4f26f8ff702f3 Mark Struberg <struberg@yahoo.de> 1197041894 +0100	push
+baa229a9193371fad604444f64c4f26f8ff702f3 1d308c3b92eb0df9c0dc76436d50edfd0ca41d18 Mark Struberg <struberg@yahoo.de> 1197042012 +0100	push
diff --git a/maven-scm-plugin/src/test/resources/git/logs/refs/remotes/origin/master b/maven-scm-plugin/src/test/resources/git/logs/refs/remotes/origin/master
new file mode 100644
index 0000000..6cb21b1
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/logs/refs/remotes/origin/master
@@ -0,0 +1 @@
+0000000000000000000000000000000000000000 c51dcd33e7b71897603c203b5e0afc1d75f70051 Mark Struberg <struberg@yahoo.de> 1196106917 +0100	clone: from /home/msx/tmp/maven-git/repository/.git
diff --git a/maven-scm-plugin/src/test/resources/git/objects/17/e953589369a48dcb0a0cbad084a76ef852cd11 b/maven-scm-plugin/src/test/resources/git/objects/17/e953589369a48dcb0a0cbad084a76ef852cd11
new file mode 100644
index 0000000..4c7bbd6
--- /dev/null
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new file mode 100644
index 0000000..7d4c247
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new file mode 100644
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new file mode 100644
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new file mode 100644
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+++ b/maven-scm-plugin/src/test/resources/git/objects/61/a0d22b023d6e31894d736cca8c1a47b6edd822
Binary files differ
diff --git a/maven-scm-plugin/src/test/resources/git/objects/92/09a983605d6e43e5cf841a1ea18a1914bb7407 b/maven-scm-plugin/src/test/resources/git/objects/92/09a983605d6e43e5cf841a1ea18a1914bb7407
new file mode 100644
index 0000000..9493985
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/objects/92/09a983605d6e43e5cf841a1ea18a1914bb7407
Binary files differ
diff --git a/maven-scm-plugin/src/test/resources/git/objects/92/f139dfec4d1dfb79c3cd2f94e83bf13129668b b/maven-scm-plugin/src/test/resources/git/objects/92/f139dfec4d1dfb79c3cd2f94e83bf13129668b
new file mode 100644
index 0000000..a352d5a
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/objects/92/f139dfec4d1dfb79c3cd2f94e83bf13129668b
@@ -0,0 +1 @@
+xÍ1Â0@QæœÂ;²›†	!.ÀÄ	\Ç¡´AÁ¸=âlyúRç¹Ð@kªàÇä1Hˆ²÷•¡äpÈQ(I Îè5qŽŽW›jƒ·;\­­£¶_¿:¿yªu—ôÔùH=}[$D'ߥé_ؕ¥Xá”ùY›¹áÚ<m
\ No newline at end of file
diff --git a/maven-scm-plugin/src/test/resources/git/objects/94/d3d586e355f318d67e3da6bb16a91be7aad1a7 b/maven-scm-plugin/src/test/resources/git/objects/94/d3d586e355f318d67e3da6bb16a91be7aad1a7
new file mode 100644
index 0000000..ea35629
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/objects/94/d3d586e355f318d67e3da6bb16a91be7aad1a7
Binary files differ
diff --git a/maven-scm-plugin/src/test/resources/git/objects/9e/131cfc732b0d9f42b9b712a528d0632d9bcca7 b/maven-scm-plugin/src/test/resources/git/objects/9e/131cfc732b0d9f42b9b712a528d0632d9bcca7
new file mode 100644
index 0000000..0ba67da
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/objects/9e/131cfc732b0d9f42b9b712a528d0632d9bcca7
Binary files differ
diff --git a/maven-scm-plugin/src/test/resources/git/objects/b5/3306f849b69ef0459ddf5cccff06b5fbb08c23 b/maven-scm-plugin/src/test/resources/git/objects/b5/3306f849b69ef0459ddf5cccff06b5fbb08c23
new file mode 100644
index 0000000..314330e
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/objects/b5/3306f849b69ef0459ddf5cccff06b5fbb08c23
Binary files differ
diff --git a/maven-scm-plugin/src/test/resources/git/objects/ba/a229a9193371fad604444f64c4f26f8ff702f3 b/maven-scm-plugin/src/test/resources/git/objects/ba/a229a9193371fad604444f64c4f26f8ff702f3
new file mode 100644
index 0000000..e94938a
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/objects/ba/a229a9193371fad604444f64c4f26f8ff702f3
@@ -0,0 +1 @@
+xÎMN1@aÖ9…÷ÈÎO“‘êXqDZÛê¤Ê¤ nBœ€ÝÛ<é“~½®|¢‡9T¡IôKòù˜„¼…¥¨ENV…«ù F™©wã¡ÛIÔ¤… ¹f*K>b¡&E6¡–“eÄDŽïóÒ¼òx‡·9îUÇž÷¿:}ñ¥÷§¦/@´dŒTJ„¢“_âÔ͎[Ó›~‡Ž}íØã¼ÎǶšÁÔ}îî™jPô
\ No newline at end of file
diff --git a/maven-scm-plugin/src/test/resources/git/objects/ba/cd4ee105073117b30e5dcdba5150373b6b53c6 b/maven-scm-plugin/src/test/resources/git/objects/ba/cd4ee105073117b30e5dcdba5150373b6b53c6
new file mode 100644
index 0000000..fe99cd8
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/objects/ba/cd4ee105073117b30e5dcdba5150373b6b53c6
Binary files differ
diff --git a/maven-scm-plugin/src/test/resources/git/objects/c3/8b0351660113545db270ba6918cc22a9eb17ce b/maven-scm-plugin/src/test/resources/git/objects/c3/8b0351660113545db270ba6918cc22a9eb17ce
new file mode 100644
index 0000000..bb5b1d5
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/objects/c3/8b0351660113545db270ba6918cc22a9eb17ce
Binary files differ
diff --git a/maven-scm-plugin/src/test/resources/git/objects/c5/1dcd33e7b71897603c203b5e0afc1d75f70051 b/maven-scm-plugin/src/test/resources/git/objects/c5/1dcd33e7b71897603c203b5e0afc1d75f70051
new file mode 100644
index 0000000..ec76cb0
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/objects/c5/1dcd33e7b71897603c203b5e0afc1d75f70051
Binary files differ
diff --git a/maven-scm-plugin/src/test/resources/git/objects/dc/4204852765c12f398ef4a5fbcabf23cf17a183 b/maven-scm-plugin/src/test/resources/git/objects/dc/4204852765c12f398ef4a5fbcabf23cf17a183
new file mode 100644
index 0000000..2234dd6
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/objects/dc/4204852765c12f398ef4a5fbcabf23cf17a183
Binary files differ
diff --git a/maven-scm-plugin/src/test/resources/git/objects/f7/1429f9ff9214a546b438c611ae942c9cf5a49e b/maven-scm-plugin/src/test/resources/git/objects/f7/1429f9ff9214a546b438c611ae942c9cf5a49e
new file mode 100644
index 0000000..b543850
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/objects/f7/1429f9ff9214a546b438c611ae942c9cf5a49e
Binary files differ
diff --git a/maven-scm-plugin/src/test/resources/git/objects/fd/39fa3de0f63bc5c78eca219e74e0a8531bd3e6 b/maven-scm-plugin/src/test/resources/git/objects/fd/39fa3de0f63bc5c78eca219e74e0a8531bd3e6
new file mode 100644
index 0000000..1497fff
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/objects/fd/39fa3de0f63bc5c78eca219e74e0a8531bd3e6
Binary files differ
diff --git a/maven-scm-plugin/src/test/resources/git/objects/fe/a16119a5b4ec0562d4f65b4237314250773bf8 b/maven-scm-plugin/src/test/resources/git/objects/fe/a16119a5b4ec0562d4f65b4237314250773bf8
new file mode 100644
index 0000000..6c36970
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/objects/fe/a16119a5b4ec0562d4f65b4237314250773bf8
Binary files differ
diff --git a/maven-scm-plugin/src/test/resources/git/refs/heads/master b/maven-scm-plugin/src/test/resources/git/refs/heads/master
new file mode 100644
index 0000000..d262065
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/refs/heads/master
@@ -0,0 +1 @@
+92f139dfec4d1dfb79c3cd2f94e83bf13129668b
diff --git a/maven-scm-plugin/src/test/resources/git/refs/remotes/origin/HEAD b/maven-scm-plugin/src/test/resources/git/refs/remotes/origin/HEAD
new file mode 100644
index 0000000..6efe28f
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/refs/remotes/origin/HEAD
@@ -0,0 +1 @@
+ref: refs/remotes/origin/master
diff --git a/maven-scm-plugin/src/test/resources/git/refs/remotes/origin/master b/maven-scm-plugin/src/test/resources/git/refs/remotes/origin/master
new file mode 100644
index 0000000..b1c9092
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/git/refs/remotes/origin/master
@@ -0,0 +1 @@
+c51dcd33e7b71897603c203b5e0afc1d75f70051
diff --git a/maven-scm-plugin/src/test/resources/mojos/untag/checkout-tag.xml b/maven-scm-plugin/src/test/resources/mojos/untag/checkout-tag.xml
new file mode 100644
index 0000000..cbf1c57
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/mojos/untag/checkout-tag.xml
@@ -0,0 +1,36 @@
+<!--
+  ~ Licensed to the Apache Software Foundation (ASF) under one
+  ~ or more contributor license agreements.  See the NOTICE file
+  ~ distributed with this work for additional information
+  ~ regarding copyright ownership.  The ASF licenses this file
+  ~ to you under the Apache License, Version 2.0 (the
+  ~ "License"); you may not use this file except in compliance
+  ~ with the License.  You may obtain a copy of the License at
+  ~
+  ~ http://www.apache.org/licenses/LICENSE-2.0
+  ~
+  ~ Unless required by applicable law or agreed to in writing,
+  ~ software distributed under the License is distributed on an
+  ~ "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+  ~ KIND, either express or implied.  See the License for the
+  ~ specific language governing permissions and limitations
+  ~ under the License.
+  -->
+
+<project>
+  <build>
+    <plugins>
+      <plugin>
+        <artifactId>maven-scm-plugin</artifactId>
+        <configuration>
+          <settings implementation="org.apache.maven.settings.Settings"/>
+          <checkoutDirectory>target/tags/mytag</checkoutDirectory>
+          <connectionType>connection</connectionType>
+          <scmVersion>mytag</scmVersion>
+          <scmVersionType>tag</scmVersionType>
+          <connectionUrl>scm:git:file:///${basedir}/target/repository</connectionUrl>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
+</project>
diff --git a/maven-scm-plugin/src/test/resources/mojos/untag/checkout.xml b/maven-scm-plugin/src/test/resources/mojos/untag/checkout.xml
new file mode 100644
index 0000000..e29441d
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/mojos/untag/checkout.xml
@@ -0,0 +1,34 @@
+<!--
+  ~ Licensed to the Apache Software Foundation (ASF) under one
+  ~ or more contributor license agreements.  See the NOTICE file
+  ~ distributed with this work for additional information
+  ~ regarding copyright ownership.  The ASF licenses this file
+  ~ to you under the Apache License, Version 2.0 (the
+  ~ "License"); you may not use this file except in compliance
+  ~ with the License.  You may obtain a copy of the License at
+  ~
+  ~ http://www.apache.org/licenses/LICENSE-2.0
+  ~
+  ~ Unless required by applicable law or agreed to in writing,
+  ~ software distributed under the License is distributed on an
+  ~ "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+  ~ KIND, either express or implied.  See the License for the
+  ~ specific language governing permissions and limitations
+  ~ under the License.
+  -->
+
+<project>
+  <build>
+    <plugins>
+      <plugin>
+        <artifactId>maven-scm-plugin</artifactId>
+        <configuration>
+          <settings implementation="org.apache.maven.settings.Settings"/>
+          <checkoutDirectory>target/tags/mytag</checkoutDirectory>
+          <connectionType>connection</connectionType>
+          <connectionUrl>scm:git:file:///${basedir}/target/repository</connectionUrl>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
+</project>
diff --git a/maven-scm-plugin/src/test/resources/mojos/untag/tag.xml b/maven-scm-plugin/src/test/resources/mojos/untag/tag.xml
new file mode 100644
index 0000000..91e2359
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/mojos/untag/tag.xml
@@ -0,0 +1,35 @@
+<!--
+  ~ Licensed to the Apache Software Foundation (ASF) under one
+  ~ or more contributor license agreements.  See the NOTICE file
+  ~ distributed with this work for additional information
+  ~ regarding copyright ownership.  The ASF licenses this file
+  ~ to you under the Apache License, Version 2.0 (the
+  ~ "License"); you may not use this file except in compliance
+  ~ with the License.  You may obtain a copy of the License at
+  ~
+  ~ http://www.apache.org/licenses/LICENSE-2.0
+  ~
+  ~ Unless required by applicable law or agreed to in writing,
+  ~ software distributed under the License is distributed on an
+  ~ "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+  ~ KIND, either express or implied.  See the License for the
+  ~ specific language governing permissions and limitations
+  ~ under the License.
+  -->
+
+<project>
+  <build>
+    <plugins>
+      <plugin>
+        <artifactId>maven-scm-plugin</artifactId>
+        <configuration>
+          <settings implementation="org.apache.maven.settings.Settings"/>
+          <connectionUrl>scm:git:file:///${basedir}/target/repository</connectionUrl>
+          <connectionType>connection</connectionType>
+          <tag>mytag</tag>
+          <pushChanges>true</pushChanges>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
+</project>
diff --git a/maven-scm-plugin/src/test/resources/mojos/untag/untag.xml b/maven-scm-plugin/src/test/resources/mojos/untag/untag.xml
new file mode 100644
index 0000000..91e2359
--- /dev/null
+++ b/maven-scm-plugin/src/test/resources/mojos/untag/untag.xml
@@ -0,0 +1,35 @@
+<!--
+  ~ Licensed to the Apache Software Foundation (ASF) under one
+  ~ or more contributor license agreements.  See the NOTICE file
+  ~ distributed with this work for additional information
+  ~ regarding copyright ownership.  The ASF licenses this file
+  ~ to you under the Apache License, Version 2.0 (the
+  ~ "License"); you may not use this file except in compliance
+  ~ with the License.  You may obtain a copy of the License at
+  ~
+  ~ http://www.apache.org/licenses/LICENSE-2.0
+  ~
+  ~ Unless required by applicable law or agreed to in writing,
+  ~ software distributed under the License is distributed on an
+  ~ "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+  ~ KIND, either express or implied.  See the License for the
+  ~ specific language governing permissions and limitations
+  ~ under the License.
+  -->
+
+<project>
+  <build>
+    <plugins>
+      <plugin>
+        <artifactId>maven-scm-plugin</artifactId>
+        <configuration>
+          <settings implementation="org.apache.maven.settings.Settings"/>
+          <connectionUrl>scm:git:file:///${basedir}/target/repository</connectionUrl>
+          <connectionType>connection</connectionType>
+          <tag>mytag</tag>
+          <pushChanges>true</pushChanges>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
+</project>
diff --git a/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-git-commons/src/main/java/org/apache/maven/scm/provider/git/AbstractGitScmProvider.java b/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-git-commons/src/main/java/org/apache/maven/scm/provider/git/AbstractGitScmProvider.java
index dbeadac..73a879c 100644
--- a/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-git-commons/src/main/java/org/apache/maven/scm/provider/git/AbstractGitScmProvider.java
+++ b/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-git-commons/src/main/java/org/apache/maven/scm/provider/git/AbstractGitScmProvider.java
@@ -40,11 +40,13 @@
 import org.apache.maven.scm.command.remove.RemoveScmResult;
 import org.apache.maven.scm.command.status.StatusScmResult;
 import org.apache.maven.scm.command.tag.TagScmResult;
+import org.apache.maven.scm.command.untag.UntagScmResult;
 import org.apache.maven.scm.command.update.UpdateScmResult;
 import org.apache.maven.scm.provider.AbstractScmProvider;
 import org.apache.maven.scm.provider.ScmProviderRepository;
 import org.apache.maven.scm.provider.git.command.GitCommand;
 import org.apache.maven.scm.provider.git.repository.GitScmProviderRepository;
+import org.apache.maven.scm.repository.ScmRepository;
 import org.apache.maven.scm.repository.ScmRepositoryException;
 import org.apache.maven.scm.repository.UnknownRepositoryStructure;
 
@@ -272,6 +274,16 @@
         return (TagScmResult) executeCommand( getTagCommand(), repository, fileSet, parameters );
     }
 
+    protected abstract GitCommand getUntagCommand();
+
+    /** {@inheritDoc} */
+    public UntagScmResult untag( ScmRepository repository, ScmFileSet fileSet, CommandParameters parameters )
+        throws ScmException
+    {
+        return (UntagScmResult) executeCommand( getUntagCommand(),
+            repository.getProviderRepository(), fileSet, parameters );
+    }
+
     protected abstract GitCommand getUpdateCommand();
 
     /** {@inheritDoc} */
diff --git a/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-git-commons/src/test/java/org/apache/maven/scm/provider/git/TestGitScmProvider.java b/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-git-commons/src/test/java/org/apache/maven/scm/provider/git/TestGitScmProvider.java
index 3f07e9a..d1f231a 100644
--- a/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-git-commons/src/test/java/org/apache/maven/scm/provider/git/TestGitScmProvider.java
+++ b/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-git-commons/src/test/java/org/apache/maven/scm/provider/git/TestGitScmProvider.java
@@ -76,6 +76,11 @@
         return null;
     }
 
+    protected GitCommand getUntagCommand()
+    {
+        return null;
+    }
+
     protected GitCommand getUpdateCommand()
     {
         return null;
diff --git a/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-gitexe/src/main/java/org/apache/maven/scm/provider/git/gitexe/GitExeScmProvider.java b/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-gitexe/src/main/java/org/apache/maven/scm/provider/git/gitexe/GitExeScmProvider.java
index 2096cad..9cb4334 100644
--- a/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-gitexe/src/main/java/org/apache/maven/scm/provider/git/gitexe/GitExeScmProvider.java
+++ b/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-gitexe/src/main/java/org/apache/maven/scm/provider/git/gitexe/GitExeScmProvider.java
@@ -38,6 +38,7 @@
 import org.apache.maven.scm.provider.git.gitexe.command.remove.GitRemoveCommand;
 import org.apache.maven.scm.provider.git.gitexe.command.status.GitStatusCommand;
 import org.apache.maven.scm.provider.git.gitexe.command.tag.GitTagCommand;
+import org.apache.maven.scm.provider.git.gitexe.command.untag.GitUntagCommand;
 import org.apache.maven.scm.provider.git.gitexe.command.update.GitUpdateCommand;
 import org.apache.maven.scm.provider.git.repository.GitScmProviderRepository;
 import org.apache.maven.scm.repository.ScmRepositoryException;
@@ -111,6 +112,12 @@
     }
 
     /** {@inheritDoc} */
+    protected GitCommand getUntagCommand()
+    {
+        return new GitUntagCommand();
+    }
+
+    /** {@inheritDoc} */
     protected GitCommand getUpdateCommand()
     {
         return new GitUpdateCommand();
diff --git a/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-gitexe/src/main/java/org/apache/maven/scm/provider/git/gitexe/command/untag/GitUntagCommand.java b/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-gitexe/src/main/java/org/apache/maven/scm/provider/git/gitexe/command/untag/GitUntagCommand.java
new file mode 100644
index 0000000..8c8798d
--- /dev/null
+++ b/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-gitexe/src/main/java/org/apache/maven/scm/provider/git/gitexe/command/untag/GitUntagCommand.java
@@ -0,0 +1,110 @@
+package org.apache.maven.scm.provider.git.gitexe.command.untag;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import java.io.File;
+
+import org.apache.maven.scm.ScmException;
+import org.apache.maven.scm.ScmFileSet;
+import org.apache.maven.scm.ScmResult;
+import org.apache.maven.scm.command.untag.AbstractUntagCommand;
+import org.apache.maven.scm.command.untag.UntagScmResult;
+import org.apache.maven.scm.provider.ScmProviderRepository;
+import org.apache.maven.scm.provider.git.command.GitCommand;
+import org.apache.maven.scm.provider.git.gitexe.command.GitCommandLineUtils;
+import org.apache.maven.scm.provider.git.repository.GitScmProviderRepository;
+import org.codehaus.plexus.util.StringUtils;
+import org.codehaus.plexus.util.cli.CommandLineUtils;
+import org.codehaus.plexus.util.cli.Commandline;
+
+/** {@inheritDoc} */
+public class GitUntagCommand
+    extends AbstractUntagCommand
+    implements GitCommand
+{
+
+    /** {@inheritDoc} */
+    public ScmResult executeUntagCommand( ScmProviderRepository repo, ScmFileSet fileSet, String tag )
+        throws ScmException
+    {
+        if ( tag == null || StringUtils.isEmpty( tag.trim() ) )
+        {
+            throw new ScmException( "tag name must be specified" );
+        }
+
+        GitScmProviderRepository repository = (GitScmProviderRepository) repo;
+
+        CommandLineUtils.StringStreamConsumer stdout = new CommandLineUtils.StringStreamConsumer();
+        CommandLineUtils.StringStreamConsumer stderr = new CommandLineUtils.StringStreamConsumer();
+
+        int exitCode;
+
+        Commandline clTag = createCommandLine( repository, fileSet.getBasedir(), tag );
+
+        exitCode = GitCommandLineUtils.execute( clTag, stdout, stderr, getLogger() );
+        if ( exitCode != 0 )
+        {
+            return new UntagScmResult( clTag.toString(), "The git-tag command failed.", stderr.getOutput(), false );
+        }
+
+        if ( repo.isPushChanges() )
+        {
+            // and now push the tag to the configured upstream repository
+            Commandline clPush = createPushCommandLine( repository, fileSet, tag );
+
+            exitCode = GitCommandLineUtils.execute( clPush, stdout, stderr, getLogger() );
+            if ( exitCode != 0 )
+            {
+                return new UntagScmResult( clPush.toString(), "The git-push command failed.", stderr.getOutput(),
+                                         false );
+            }
+        }
+
+        return new UntagScmResult( clTag.toString() );
+    }
+
+    // ----------------------------------------------------------------------
+    //
+    // ----------------------------------------------------------------------
+
+    public static Commandline createCommandLine( GitScmProviderRepository repository, File workingDirectory,
+                                                 String tag )
+    {
+        Commandline cl = GitCommandLineUtils.getBaseGitCommandLine( workingDirectory, "tag" );
+
+        cl.createArg().setValue( "-d" );
+        cl.createArg().setValue( tag );
+
+        return cl;
+    }
+
+    public static Commandline createPushCommandLine( GitScmProviderRepository repository, ScmFileSet fileSet,
+                                                     String tag )
+    {
+        Commandline cl = GitCommandLineUtils.getBaseGitCommandLine( fileSet.getBasedir(), "push" );
+
+        cl.createArg().setValue( "--delete" );
+        cl.createArg().setValue( repository.getPushUrl() );
+        cl.createArg().setValue( "refs/tags/" + tag );
+
+        return cl;
+    }
+
+}
diff --git a/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-gitexe/src/test/java/org/apache/maven/scm/provider/git/gitexe/command/untag/GitExeUntagCommandTckTest.java b/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-gitexe/src/test/java/org/apache/maven/scm/provider/git/gitexe/command/untag/GitExeUntagCommandTckTest.java
new file mode 100644
index 0000000..0a19847
--- /dev/null
+++ b/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-gitexe/src/test/java/org/apache/maven/scm/provider/git/gitexe/command/untag/GitExeUntagCommandTckTest.java
@@ -0,0 +1,34 @@
+package org.apache.maven.scm.provider.git.gitexe.command.untag;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import org.apache.maven.scm.provider.git.GitScmTestUtils;
+import org.apache.maven.scm.provider.git.command.untag.GitUntagCommandTckTest;
+
+public class GitExeUntagCommandTckTest
+    extends GitUntagCommandTckTest
+{
+        /** {@inheritDoc} */
+        public String getScmUrl()
+            throws Exception
+        {
+            return GitScmTestUtils.getScmUrl( getRepositoryRoot(), "git" );
+        }
+}
diff --git a/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-gittest/src/main/java/org/apache/maven/scm/provider/git/command/untag/GitUntagCommandTckTest.java b/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-gittest/src/main/java/org/apache/maven/scm/provider/git/command/untag/GitUntagCommandTckTest.java
new file mode 100644
index 0000000..7eff053
--- /dev/null
+++ b/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-gittest/src/main/java/org/apache/maven/scm/provider/git/command/untag/GitUntagCommandTckTest.java
@@ -0,0 +1,51 @@
+package org.apache.maven.scm.provider.git.command.untag;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import java.io.File;
+import org.apache.maven.scm.command.checkout.CheckOutScmResult;
+import org.apache.maven.scm.provider.git.GitScmTestUtils;
+import org.apache.maven.scm.repository.ScmRepository;
+import org.apache.maven.scm.tck.command.untag.UntagCommandTckTest;
+
+/** {@inheritDoc} */
+public abstract class GitUntagCommandTckTest
+    extends UntagCommandTckTest
+{
+    /** {@inheritDoc} */
+    public void initRepo()
+        throws Exception
+    {
+        GitScmTestUtils.initRepo( "src/test/resources/repository/", getRepositoryRoot(), getWorkingDirectory() );
+    }
+
+    @Override
+    protected CheckOutScmResult checkOut( File workingDirectory, ScmRepository repository ) throws Exception
+    {
+        try
+        {
+            return super.checkOut( workingDirectory, repository );
+        }
+        finally
+        {
+            GitScmTestUtils.setDefaultUser( workingDirectory );
+        }
+    }
+}
diff --git a/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-jgit/src/main/java/org/apache/maven/scm/provider/git/jgit/JGitScmProvider.java b/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-jgit/src/main/java/org/apache/maven/scm/provider/git/jgit/JGitScmProvider.java
index b155dea..0c6d351 100644
--- a/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-jgit/src/main/java/org/apache/maven/scm/provider/git/jgit/JGitScmProvider.java
+++ b/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-jgit/src/main/java/org/apache/maven/scm/provider/git/jgit/JGitScmProvider.java
@@ -39,6 +39,7 @@
 import org.apache.maven.scm.provider.git.jgit.command.remoteinfo.JGitRemoteInfoCommand;
 import org.apache.maven.scm.provider.git.jgit.command.status.JGitStatusCommand;
 import org.apache.maven.scm.provider.git.jgit.command.tag.JGitTagCommand;
+import org.apache.maven.scm.provider.git.jgit.command.untag.JGitUntagCommand;
 import org.apache.maven.scm.repository.ScmRepositoryException;
 
 /**
@@ -133,6 +134,14 @@
     /**
      * {@inheritDoc}
      */
+    protected GitCommand getUntagCommand()
+    {
+        return new JGitUntagCommand();
+    }
+
+    /**
+     * {@inheritDoc}
+     */
     protected GitCommand getUpdateCommand()
     {
         throw new UnsupportedOperationException( "getUpdateCommand" );
diff --git a/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-jgit/src/main/java/org/apache/maven/scm/provider/git/jgit/command/untag/JGitUntagCommand.java b/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-jgit/src/main/java/org/apache/maven/scm/provider/git/jgit/command/untag/JGitUntagCommand.java
new file mode 100644
index 0000000..3cc629e
--- /dev/null
+++ b/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-jgit/src/main/java/org/apache/maven/scm/provider/git/jgit/command/untag/JGitUntagCommand.java
@@ -0,0 +1,102 @@
+package org.apache.maven.scm.provider.git.jgit.command.untag;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import java.util.Collection;
+
+import org.apache.maven.scm.ScmException;
+import org.apache.maven.scm.ScmFileSet;
+import org.apache.maven.scm.ScmResult;
+import org.apache.maven.scm.command.untag.AbstractUntagCommand;
+import org.apache.maven.scm.command.untag.UntagScmResult;
+import org.apache.maven.scm.log.ScmLogger;
+import org.apache.maven.scm.provider.ScmProviderRepository;
+import org.apache.maven.scm.provider.git.command.GitCommand;
+import org.apache.maven.scm.provider.git.jgit.command.JGitUtils;
+import org.apache.maven.scm.provider.git.repository.GitScmProviderRepository;
+import org.codehaus.plexus.util.StringUtils;
+import org.eclipse.jgit.api.Git;
+import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.transport.PushResult;
+import org.eclipse.jgit.transport.RefSpec;
+import org.eclipse.jgit.transport.RemoteRefUpdate;
+
+/** {@inheritDoc} */
+public class JGitUntagCommand extends AbstractUntagCommand implements GitCommand
+{
+
+    @Override
+    protected ScmResult executeUntagCommand( ScmProviderRepository repository, ScmFileSet fileSet,
+        String tagName ) throws ScmException
+    {
+        if ( tagName == null || StringUtils.isEmpty( tagName.trim() ) )
+        {
+            throw new ScmException( "tag name must be specified" );
+        }
+        String escapedTagName = tagName.trim().replace( ' ', '_' );
+
+        Git git = null;
+        try
+        {
+            git = JGitUtils.openRepo( fileSet.getBasedir() );
+
+            // delete the tag
+            if ( git.tagDelete().setTags( escapedTagName ).call().isEmpty() )
+            {
+                return new UntagScmResult( "JGit tagDelete", "Failed to delete tag", "", false );
+            }
+
+            if ( repository.isPushChanges() )
+            {
+                // From https://stackoverflow.com/q/11892766/696632
+                RefSpec refSpec = new RefSpec()
+                    .setSource( null )
+                    .setDestination( Constants.R_TAGS + escapedTagName );
+
+                getLogger().info( "push delete tag [" + escapedTagName + "] to remote..." );
+                ScmLogger logger = getLogger();
+
+                Iterable<PushResult> pushResultList
+                        = JGitUtils.push( logger, git, (GitScmProviderRepository) repository, refSpec );
+                if ( logger.isInfoEnabled() )
+                {
+                    for ( PushResult pushResult : pushResultList )
+                    {
+                        Collection<RemoteRefUpdate> ru = pushResult.getRemoteUpdates();
+                        for ( RemoteRefUpdate remoteRefUpdate : ru )
+                        {
+                            logger.info( remoteRefUpdate.getStatus() + " - " + remoteRefUpdate );
+                        }
+                    }
+                }
+            }
+
+            return new UntagScmResult( "JGit tagDelete" );
+        }
+        catch ( Exception e )
+        {
+            throw new ScmException( "JGit tagDelete failure!", e );
+        }
+        finally
+        {
+            JGitUtils.closeRepo( git );
+        }
+    }
+}
diff --git a/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-jgit/src/test/java/org/apache/maven/scm/provider/git/jgit/command/untag/JGitUntagCommandTckTest.java b/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-jgit/src/test/java/org/apache/maven/scm/provider/git/jgit/command/untag/JGitUntagCommandTckTest.java
new file mode 100644
index 0000000..268ef41
--- /dev/null
+++ b/maven-scm-providers/maven-scm-providers-git/maven-scm-provider-jgit/src/test/java/org/apache/maven/scm/provider/git/jgit/command/untag/JGitUntagCommandTckTest.java
@@ -0,0 +1,52 @@
+package org.apache.maven.scm.provider.git.jgit.command.untag;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import java.io.File;
+import java.io.IOException;
+import org.apache.maven.scm.provider.git.GitScmTestUtils;
+import org.apache.maven.scm.provider.git.command.untag.GitUntagCommandTckTest;
+import org.eclipse.jgit.util.FileUtils;
+
+/**
+ * This test tests the untag command.
+ */
+public class JGitUntagCommandTckTest
+    extends GitUntagCommandTckTest
+{
+    /**
+     * {@inheritDoc}
+     */
+    public String getScmUrl()
+        throws Exception
+    {
+        return GitScmTestUtils.getScmUrl( getRepositoryRoot(), "jgit" );
+    }
+
+    @Override
+    protected void deleteDirectory( File directory )
+        throws IOException
+    {
+        if ( directory.exists() )
+        {
+            FileUtils.delete( directory, FileUtils.RECURSIVE | FileUtils.RETRY );
+        }
+    }
+}
diff --git a/maven-scm-test/src/main/java/org/apache/maven/scm/provider/ScmProviderStub.java b/maven-scm-test/src/main/java/org/apache/maven/scm/provider/ScmProviderStub.java
index 9edf2c2..2b6c284 100644
--- a/maven-scm-test/src/main/java/org/apache/maven/scm/provider/ScmProviderStub.java
+++ b/maven-scm-test/src/main/java/org/apache/maven/scm/provider/ScmProviderStub.java
@@ -46,6 +46,7 @@
 import org.apache.maven.scm.command.status.StatusScmResult;
 import org.apache.maven.scm.command.tag.TagScmResult;
 import org.apache.maven.scm.command.unedit.UnEditScmResult;
+import org.apache.maven.scm.command.untag.UntagScmResult;
 import org.apache.maven.scm.command.update.UpdateScmResult;
 import org.apache.maven.scm.log.ScmLogger;
 import org.apache.maven.scm.repository.ScmRepository;
@@ -113,6 +114,8 @@
 
     private MkdirScmResult mkdirScmResult;
 
+    private UntagScmResult untagScmResult;
+
     /**
      * Create a new ScmProviderStub with bogus (not null) attributes
      */
@@ -131,6 +134,7 @@
         setStatusScmResult( new StatusScmResult( "", "", "", true ) );
         setTagScmResult( new TagScmResult( "", "", "", true ) );
         setUnEditScmResult( new UnEditScmResult( "", "", "", true ) );
+        setUntagScmResult( new UntagScmResult( "", "", "", true ) );
         setUpdateScmResult( new UpdateScmResult( "", "", "", true ) );
         setBlameScmResult( new BlameScmResult( "", "", "", true ) );
         setMkdirScmResult( new MkdirScmResult( "", "", "", true ) );
@@ -258,6 +262,16 @@
         return tagScmResult;
     }
 
+    public void setUntagScmResult( UntagScmResult untagScmResult )
+    {
+        this.untagScmResult = untagScmResult;
+    }
+
+    public UntagScmResult getUntagScmResult()
+    {
+        return untagScmResult;
+    }
+
     public void setRemoveScmResult( RemoveScmResult removeScmResult )
     {
         this.removeScmResult = removeScmResult;
@@ -745,6 +759,12 @@
         return getTagScmResult();
     }
 
+    public UntagScmResult untag( ScmRepository repository, ScmFileSet fileSet, CommandParameters parameters )
+        throws ScmException
+    {
+        return getUntagScmResult();
+    }
+
     /**
      * {@inheritDoc}
      */
diff --git a/maven-scm-test/src/main/java/org/apache/maven/scm/tck/command/untag/UntagCommandTckTest.java b/maven-scm-test/src/main/java/org/apache/maven/scm/tck/command/untag/UntagCommandTckTest.java
new file mode 100644
index 0000000..2968cac
--- /dev/null
+++ b/maven-scm-test/src/main/java/org/apache/maven/scm/tck/command/untag/UntagCommandTckTest.java
@@ -0,0 +1,84 @@
+package org.apache.maven.scm.tck.command.untag;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import org.apache.maven.scm.CommandParameter;
+import org.apache.maven.scm.CommandParameters;
+import org.apache.maven.scm.ScmException;
+import org.apache.maven.scm.ScmFileSet;
+import org.apache.maven.scm.ScmTag;
+import org.apache.maven.scm.ScmTagParameters;
+import org.apache.maven.scm.ScmTckTestCase;
+import org.apache.maven.scm.command.checkout.CheckOutScmResult;
+import org.apache.maven.scm.command.tag.TagScmResult;
+import org.apache.maven.scm.command.untag.UntagScmResult;
+import org.apache.maven.scm.provider.ScmProvider;
+import org.apache.maven.scm.repository.ScmRepository;
+
+/**
+ * This test tests the untag command.
+ */
+public abstract class UntagCommandTckTest
+    extends ScmTckTestCase
+{
+
+    protected String getTagName()
+    {
+        return "test-untag";
+    }
+
+    public void testUntagCommandTest()
+        throws Exception
+    {
+        String tag = getTagName();
+        ScmProvider scmProvider = getScmManager().getProviderByUrl( getScmUrl() );
+        ScmRepository scmRepository = getScmRepository();
+        ScmFileSet files = new ScmFileSet( getWorkingCopy() );
+        TagScmResult tagResult = scmProvider.tag( scmRepository, files, tag, new ScmTagParameters() );
+
+        assertResultIsSuccess( tagResult );
+        CommandParameters params = new CommandParameters();
+        params.setString( CommandParameter.TAG_NAME, tag );
+
+        UntagScmResult untagResult = scmProvider.untag( scmRepository, files, params );
+
+        assertResultIsSuccess( untagResult );
+
+        try
+        {
+            untagResult = scmProvider.untag( scmRepository, files, params );
+            assertFalse( untagResult.isSuccess() ); // already been deleted
+        }
+        catch ( ScmException ignored )
+        {
+        }
+
+        try
+        {
+            CheckOutScmResult checkoutResult =
+                getScmManager().checkOut( scmRepository, new ScmFileSet( getAssertionCopy() ), new ScmTag( tag ) );
+            assertFalse( checkoutResult.isSuccess() ); // can't check out a deleted tags
+        }
+        catch ( ScmException ignored )
+        {
+        }
+    }
+
+}