diff --git a/.plzconfig b/.plzconfig
index eb59b60..bf168eb 100644
--- a/.plzconfig
+++ b/.plzconfig
@@ -93,5 +93,11 @@ Help = The maven repo to use for maven_jar
 [PluginConfig "home"]
 ConfigKey = Home
 Optional = true
-Help = Sets the java home variable 
+Help = Sets the java home variable
 Inherit = True
+
+[PluginConfig "require_licences"]
+DefaultValue = false
+Type = bool
+Inherit = true
+Help = If set, the licences field on maven_jar will be mandatory
diff --git a/ChangeLog b/ChangeLog
index 544a370..01fdbd4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Version 0.4.6
+-------------
+    * Add `require_licences` to plugin config
+
 Version 0.4.5
 -------------
     * fix `java_test` using f-string to test package arg
diff --git a/README.md b/README.md
index aa269ae..87a02fa 100644
--- a/README.md
+++ b/README.md
@@ -1,9 +1,9 @@
-# Java rules 
+# Java rules
 
 This repo provides Java rules for the [please](https://please.build) build system.
 
 # Basic usage
-See `./example` in this repo for a working example. 
+See `./example` in this repo for a working example.
 
 ```python
 # BUILD
@@ -23,18 +23,18 @@ java_library(
 )
 
 # src/test/java/build/please/foo/BUILD
-# A test for the above library. 
+# A test for the above library.
 java_test(
     name = "foo_test",
     srcs = ["FooTest.java"],
     deps = [
-        "//third_party/java:junit", 
+        "//third_party/java:junit",
         "//src/main/java/build/please/foo",
     ]
 )
 
 # src/main/java/build/please/foo/BUILD
-# This produces a self-executing .jar 
+# This produces a self-executing .jar
 java_binary(
     name = "app",
     main_class = "build.please.Main",
@@ -43,7 +43,7 @@ java_binary(
 )
 
 # third_party/java/BUILD
-# These rules pull down third party dependencies from maven. 
+# These rules pull down third party dependencies from maven.
 maven_jar(
     name = "junit",
     hash = "59721f0805e223d84b90677887d9ff567dc534d7c502ca903c0c2b17f05c116a",
@@ -65,8 +65,8 @@ Then add this to your `.plzconfig`:
 [Parse]
 PreloadSubincludes = @java_rules//build_defs:java
 ```
-Alternatively, if you're not using Java everywhere, you may add `subinclude("@java_rules//build_defs:java")` to each 
-BUILD individually. 
+Alternatively, if you're not using Java everywhere, you may add `subinclude("@java_rules//build_defs:java")` to each
+BUILD individually.
 
 ## Toolchain
 By default, Please will use the JDK on the path. Optionally, you may use `java_toolchain()` to manage your JDK:
@@ -92,9 +92,9 @@ Plugins are configured through the Plugin section like so:
 SomeConfig = some value
 ```
 
-The available configuration options for this plugin are documented here. 
+The available configuration options for this plugin are documented here.
 
-## JavacTool 
+## JavacTool
 The path to the Java compiler to use. Defaults to `javac`.
 
 ```
@@ -103,7 +103,7 @@ JavacTool = /opt/java/bin/javac
 ```
 
 ## JavacFlags
-Any additional flags to apply to the javac tool. 
+Any additional flags to apply to the javac tool.
 
 ```
 [Plugin "java"]
@@ -111,7 +111,7 @@ JavacFalgs = --flag1 --flag2
 ```
 
 ## JavacTestFlags
-Any additional flags to apply to the javac tool when compiling tests. 
+Any additional flags to apply to the javac tool when compiling tests.
 
 ```
 [Plugin "java"]
@@ -119,7 +119,7 @@ TestJavacFlags = --flag1 --flag2
 ```
 
 ## JunitRunner
-The tool used to run Java tests. Defaults to the junit runner for this plugin version 
+The tool used to run Java tests. Defaults to the junit runner for this plugin version
 i.e. `@java_rules//tools:junit_runner`
 
 ```
@@ -135,7 +135,7 @@ JunitRunner = //tools:my_custom_junit_runner
 ```
 
 ## SourceLevel
-The source level of the project. Defaults to 8. 
+The source level of the project. Defaults to 8.
 ```
 [Plugin "java"]
 SourceLevel = 15
@@ -156,7 +156,7 @@ ReleaseLevel = 15
 ```
 
 ## Toolchain
-If set, please will use the jdk provided by the `java_toolchain()` rule specified by this build label. See the toolchain 
+If set, please will use the jdk provided by the `java_toolchain()` rule specified by this build label. See the toolchain
 section above for more info.
 
 ```
@@ -166,7 +166,7 @@ Toolchain = //third_party/java:toolchain
 
 ## DefaultTestPackage
 The test package to use when none is specifically set on the `java_test()` rule. If not set, Please will run all tests
-present in the `.jar` that are not from third party code. 
+present in the `.jar` that are not from third party code.
 
 ```
 [Plugin "java"]
@@ -174,8 +174,8 @@ DefaultTestPackage = please.build.
 ```
 
 ## MavenRepo
-The maven repositories to load jars from. This value can be repeated and defaults to `https://repo1.maven.org/maven2` 
-and `https://repo.maven.apache.org/maven2`, the canonical Maven Central repository URLs. 
+The maven repositories to load jars from. This value can be repeated and defaults to `https://repo1.maven.org/maven2`
+and `https://repo.maven.apache.org/maven2`, the canonical Maven Central repository URLs.
 
 To add a custom repo, you may do so by setting the following:
 
@@ -185,3 +185,11 @@ MavenRepo = https://repo1.maven.org/maven2
 MavenRepo = https://repo.maven.apache.org/maven2
 MavenRepo = https://maven.repo.org
 ```
+
+## RequireLicences
+To require licences for Mavan jars, you set the `RequireLicences` option to true.
+
+```
+[Plugin "java"]
+RequireLicences = true
+```
diff --git a/VERSION b/VERSION
index 0bfccb0..8f0916f 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-0.4.5
+0.5.0
diff --git a/build_defs/java.build_defs b/build_defs/java.build_defs
index fafdeec..51f19be 100644
--- a/build_defs/java.build_defs
+++ b/build_defs/java.build_defs
@@ -534,6 +534,12 @@ def maven_jar(name:str, id:str, repository:str|list=None, labels:list=[], hash:s
 
 def _parse_maven_artifact(id, sources=True, licences=None):
     """Parses a Maven artifact in group:artifact:version format, with possibly some extras."""
+
+    if not licences:
+        msg = f'No licence found for {id}, should add licences = [...] to the rule'
+        if CONFIG.JAVA.REQUIRE_LICENCES:
+            fail(msg)
+
     parts = id.split(':')
     if len(parts) == 5:
         group, artifact, version = parts[:3]
diff --git a/third_party/java/BUILD b/third_party/java/BUILD
index bdf9854..589a1f9 100644
--- a/third_party/java/BUILD
+++ b/third_party/java/BUILD
@@ -23,18 +23,27 @@ maven_jar(
     deps = [
         ":hamcrest",
     ],
+    licences = [
+        "EPL-1.0",
+    ],
 )
 
 maven_jar(
     name = "hamcrest",
     hash = "4877670629ab96f34f5f90ab283125fcd9acb7e683e66319a68be6eb2cca60de",
     id = "org.hamcrest:hamcrest-all:1.3",
+    licences = [
+        "BSD-3-Clause",
+    ],
 )
 
 maven_jar(
     name = "gson",
     hash = "53bc5fe7644db908e6071d6c8b59059acadce7fc14217933d7251994e8673104",
     id = "com.google.code.gson:gson:2.8.4",
+    licences = [
+        "Apache-2.0",
+    ],
 )
 
 # These are shipped as components of Please, but for easier management the code lives in
@@ -49,12 +58,18 @@ maven_jar(
         ":jacoco_shaded",
         ":junit",
     ],
+    licences = [
+        "Apache-2.0",
+    ],
 )
 
 maven_jar(
     name = "jacoco_shaded",
     hashes = ["9927bc9184d434c8ed0ed7ba46257df36e31dbd6bd224845d7a02d9e0894da4c"],
     id = "build.please:jacoco-shaded:0.8.4",
+    licences = [
+        "Apache-2.0",
+    ]
 )
 
 maven_jar(
@@ -66,6 +81,10 @@ maven_jar(
         ":logback-core",
         ":slf4j-api",
     ],
+    licences = [
+        "EPL-1.0",
+        "LGPL-2.1-only",
+    ],
 )
 
 maven_jar(
@@ -73,6 +92,10 @@ maven_jar(
     hash = "47c0fd342995d3315b8faccacc324b2a76143b27c430d4b2d6a29eabc31f5c14",
     id = "ch.qos.logback:logback-core:1.1.3",
     test_only = True,
+    licences = [
+        "EPL-1.0",
+        "LGPL-2.1-only",
+    ],
 )
 
 maven_jar(
@@ -80,4 +103,7 @@ maven_jar(
     hash = "3863e27005740d4d1289bf87b113efea115e9a22408a7d623be8004991232bfe",
     id = "org.slf4j:slf4j-api:1.7.10",
     test_only = True,
+    licences = [
+        "MIT",
+    ]
 )