diff --git a/changelog.html b/changelog.html
index db0ddfc1bdc6feb2540c353505f05f74f9d4518b..9620b517a525333affc129e4dcb6c345aa225e0c 100644
--- a/changelog.html
+++ b/changelog.html
@@ -84,6 +84,10 @@ Upcoming changes</a>
   <li class=bug>
     Global search box now remembers entered text
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-18192">issue 18192</a>)
+  <li class=rfe>
+    Add extension point to allow plugins to contribute to the checking of
+    assigned labels.
+    (<a href="https://issues.jenkins-ci.org/browse/JENKINS-20514">issue 20514</a>)
 </ul>
 </div><!--=TRUNK-END=-->
 
diff --git a/core/src/main/java/hudson/model/AbstractProject.java b/core/src/main/java/hudson/model/AbstractProject.java
index 32584041b4420ccac9f6285f0edf0231d68b4df7..7321e88096d058e05deb9b083640ba0ea6a3db84 100644
--- a/core/src/main/java/hudson/model/AbstractProject.java
+++ b/core/src/main/java/hudson/model/AbstractProject.java
@@ -29,6 +29,7 @@ package hudson.model;
 
 import com.infradna.tool.bridge_method_injector.WithBridgeMethods;
 import hudson.EnvVars;
+import hudson.ExtensionPoint;
 import hudson.Functions;
 import antlr.ANTLRException;
 import hudson.AbortException;
@@ -103,6 +104,7 @@ import org.kohsuke.accmod.restrictions.NoExternalUse;
 import org.kohsuke.args4j.Argument;
 import org.kohsuke.args4j.CmdLineException;
 import org.kohsuke.stapler.Ancestor;
+import org.kohsuke.stapler.AncestorInPath;
 import org.kohsuke.stapler.ForwardToView;
 import org.kohsuke.stapler.HttpRedirect;
 import org.kohsuke.stapler.HttpResponse;
@@ -2209,7 +2211,8 @@ public abstract class AbstractProject<P extends AbstractProject<P,R>,R extends A
             return true;
         }
 
-        public FormValidation doCheckAssignedLabelString(@QueryParameter String value) {
+        public FormValidation doCheckAssignedLabelString(@AncestorInPath AbstractProject<?,?> project,
+                                                         @QueryParameter String value) {
             if (Util.fixEmpty(value)==null)
                 return FormValidation.ok(); // nothing typed yet
             try {
@@ -2228,6 +2231,15 @@ public abstract class AbstractProject<P extends AbstractProject<P,R>,R extends A
                 }
                 return FormValidation.warning(Messages.AbstractProject_AssignedLabelString_NoMatch());
             }
+            if (project != null) {
+                for (AbstractProject.LabelValidator v : Jenkins.getInstance()
+                        .getExtensionList(AbstractProject.LabelValidator.class)) {
+                    FormValidation result = v.check(project, l);
+                    if (!FormValidation.Kind.OK.equals(result.kind)) {
+                        return result;
+                    }
+                }
+            }
             return FormValidation.ok();
         }
 
@@ -2384,5 +2396,23 @@ public abstract class AbstractProject<P extends AbstractProject<P,R>,R extends A
         this.customWorkspace= Util.fixEmptyAndTrim(customWorkspace);
         save();
     }
-    
+
+    /**
+     * Plugins may want to contribute additional restrictions on the use of specific labels for specific projects.
+     * This extension point allows such restrictions.
+     *
+     * @since 1.540
+     */
+    public static abstract class LabelValidator implements ExtensionPoint {
+        /**
+         * Check the use of the label within the specified context.
+         *
+         * @param project the project that wants to restrict itself to the specified label.
+         * @param label   the label that the project wants to restrict itself to.
+         * @return the {@link FormValidation} result.
+         */
+        @Nonnull
+        public abstract FormValidation check(@Nonnull AbstractProject<?, ?> project, @Nonnull Label label);
+    }
+
 }
diff --git a/test/src/test/java/hudson/model/labels/LabelExpressionTest.java b/test/src/test/java/hudson/model/labels/LabelExpressionTest.java
index f2df9b967314f59716c2156800480a20c54a18b3..d75e892567ff9c3166ce6e63e66a687354cae155 100644
--- a/test/src/test/java/hudson/model/labels/LabelExpressionTest.java
+++ b/test/src/test/java/hudson/model/labels/LabelExpressionTest.java
@@ -233,11 +233,11 @@ public class LabelExpressionTest extends HudsonTestCase {
 
                 Label l = jenkins.getLabel("foo");
                 DumbSlave s = createSlave(l);
-                String msg = d.doCheckAssignedLabelString("goo").renderHtml();
+                String msg = d.doCheckAssignedLabelString(null, "goo").renderHtml();
                 assertTrue(msg.contains("foo"));
                 assertTrue(msg.contains("goo"));
 
-                msg = d.doCheckAssignedLabelString("master && goo").renderHtml();
+                msg = d.doCheckAssignedLabelString(null, "master && goo").renderHtml();
                 assertTrue(msg.contains("foo"));
                 assertTrue(msg.contains("goo"));
                 return null;