diff --git a/README.md b/README.md
index 6accd8e..2724e97 100644
--- a/README.md
+++ b/README.md
@@ -21,6 +21,9 @@ DiscourseGroupSync has several options that can be configured in the `config.yml
 # The URL of your Discourse installation (without the trailing slash)
 discourse-url: http://forum.example.com
 
+# Message to display if kicking due to whitelist
+kick-message: You are not on the whitelist
+
 # A mapping between Discourse groups (by integer ID) and Minecraft groups (by name)
 groups:
 
@@ -40,6 +43,8 @@ groups:
 
 `discourse` keys are the IDs of your chosen Discourse groups.  A negative number means the absence of the group, so `discourse: -20` would target users who were not a member of group `20`.  `0` is a special group meaning users who are not a member of any Discourse groups.
 
+Set a `whitelist: true` field on any of the groups to enable them as a whitelist filter.
+
 ## Features
 
 * Synchronizes Minecraft groups with Discourse groups on player join
diff --git a/pom.xml b/pom.xml
index 7cff417..82844a0 100644
--- a/pom.xml
+++ b/pom.xml
@@ -31,10 +31,6 @@
             <id>vault-repo</id>
             <url>http://nexus.theyeticave.net/content/repositories/pub_releases</url>
         </repository>
-        <repository>
-            <id>jitpack.io</id>
-            <url>https://jitpack.io</url>
-        </repository>
     </repositories>
 
     <dependencies>
diff --git a/src/main/kotlin/gg/obsidian/discoursegroupsync/Configuration.kt b/src/main/kotlin/gg/obsidian/discoursegroupsync/Configuration.kt
index 6f8bf90..9101cd3 100644
--- a/src/main/kotlin/gg/obsidian/discoursegroupsync/Configuration.kt
+++ b/src/main/kotlin/gg/obsidian/discoursegroupsync/Configuration.kt
@@ -5,18 +5,21 @@ import java.util.*
 class Configuration(val plugin: DiscourseGroupSync) {
 
     var DISCOURSE_URL = ""
+    var KICK_MESSAGE = ""
     var GROUPS: HashSet<Group> = HashSet<Group>()
 
     fun load() {
         plugin.reloadConfig()
 
         DISCOURSE_URL = plugin.getConfig().getString("discourse-url")
+        KICK_MESSAGE = plugin.getConfig().getString("kick-message", "You are not on the whitelist")
 
         for (rawDefinition in plugin.getConfig().getMapList("groups")) {
             val definition = rawDefinition as Map<String, Any>
             var discourseGroup: Int? = null
             var minecraftGroup: String? = null
             var remove = false
+            var whitelist = false
 
             if (definition.contains("discourse")) {
                 discourseGroup = definition["discourse"] as Int
@@ -30,9 +33,18 @@ class Configuration(val plugin: DiscourseGroupSync) {
                 remove = definition["remove"] as Boolean
             }
 
+            if (definition.contains("whitelist")) {
+                whitelist = definition["whitelist"] as Boolean
+            }
+
             if (discourseGroup == null || minecraftGroup == null) continue
 
-            val group = Group(discourseGroup, minecraftGroup, remove)
+            val group = Group(
+                    discourseGroup = discourseGroup,
+                    minecraftGroup = minecraftGroup,
+                    remove = remove,
+                    whitelist = whitelist
+            )
             GROUPS.add(group)
         }
     }
diff --git a/src/main/kotlin/gg/obsidian/discoursegroupsync/DiscourseGroupSync.kt b/src/main/kotlin/gg/obsidian/discoursegroupsync/DiscourseGroupSync.kt
index 40171fa..5b23832 100644
--- a/src/main/kotlin/gg/obsidian/discoursegroupsync/DiscourseGroupSync.kt
+++ b/src/main/kotlin/gg/obsidian/discoursegroupsync/DiscourseGroupSync.kt
@@ -34,7 +34,10 @@ class DiscourseGroupSync : JavaPlugin(), Listener {
 
     @EventHandler
     fun onJoin(e: PlayerJoinEvent) {
-        userManager.syncGroups(e.player)
+        val canJoin = userManager.onJoin(e.player)
+        if (!canJoin) {
+            e.player.kickPlayer(config.KICK_MESSAGE)
+        }
     }
 
     fun setupPermissions(): Boolean {
diff --git a/src/main/kotlin/gg/obsidian/discoursegroupsync/Group.kt b/src/main/kotlin/gg/obsidian/discoursegroupsync/Group.kt
index 7b5b204..288c485 100644
--- a/src/main/kotlin/gg/obsidian/discoursegroupsync/Group.kt
+++ b/src/main/kotlin/gg/obsidian/discoursegroupsync/Group.kt
@@ -1,3 +1,8 @@
 package gg.obsidian.discoursegroupsync
 
-data class Group(val discourseGroup: Int, val minecraftGroup: String, val remove: Boolean = false)
+data class Group(
+        val discourseGroup: Int,
+        val minecraftGroup: String,
+        val remove: Boolean = false,
+        val whitelist: Boolean = false
+)
diff --git a/src/main/kotlin/gg/obsidian/discoursegroupsync/UserManger.kt b/src/main/kotlin/gg/obsidian/discoursegroupsync/UserManger.kt
index b190007..5b9db28 100644
--- a/src/main/kotlin/gg/obsidian/discoursegroupsync/UserManger.kt
+++ b/src/main/kotlin/gg/obsidian/discoursegroupsync/UserManger.kt
@@ -12,7 +12,17 @@ class UserManager(val plugin: DiscourseGroupSync) {
 
     val httpClient = OkHttpClient()
 
-    fun getDiscourseUser(username: String): User {
+    fun onJoin(player: Player): Boolean {
+        val user = getDiscourseUser(player)
+
+        syncGroups(player, user)
+        return checkWhitelist(user)
+    }
+
+    fun getDiscourseUser(player: Player): User? {
+        val username = UUIDHelper.uuidToUsername(player.uniqueId)
+        if (username == "") return null
+
         val url = plugin.config.DISCOURSE_URL + "/users/" + username + ".json"
         val request = Request.Builder().url(url).get().build();
         val response = httpClient.newCall(request).execute()
@@ -41,12 +51,32 @@ class UserManager(val plugin: DiscourseGroupSync) {
         return User(username = username, discourseGroups = discourseGroups)
     }
 
-    fun syncGroups(player: Player) {
-        val username = UUIDHelper.uuidToUsername(player.uniqueId)
-        if (username == "") return
+    fun checkWhitelist(user: User?): Boolean {
+        if (user == null) {
+            for (group in plugin.config.GROUPS) {
+                if (group.whitelist == true)
+                    return false
+            }
+            return true
+        }
 
-        val user = getDiscourseUser(username)
+        var canJoin = true
+
+        for (group in plugin.config.GROUPS) {
+            if (group.whitelist != true) continue
+
+            if (user.discourseGroups.contains(group.discourseGroup)) {
+                return true
+            } else {
+                canJoin = false
+            }
+        }
+
+        return canJoin
+    }
 
+    fun syncGroups(player: Player, user: User?) {
+        if (user == null) return
         val groupsToAdd = HashSet<String>()
         val groupsToRemove = HashSet<String>()
 
@@ -82,12 +112,12 @@ class UserManager(val plugin: DiscourseGroupSync) {
         }
 
         for (group in groupsToAdd) {
-            plugin.logger.info("Adding $username to group $group")
+            plugin.logger.info("Adding ${user.username} to group $group")
             plugin.permissions?.playerAddGroup(player, group)
         }
 
         for (group in groupsToRemove) {
-            plugin.logger.info("Removing $username from group $group")
+            plugin.logger.info("Removing ${user.username} from group $group")
             plugin.permissions?.playerRemoveGroup(player, group)
         }
     }
diff --git a/src/main/resources/config.yml b/src/main/resources/config.yml
index dace8d5..c92a1bc 100644
--- a/src/main/resources/config.yml
+++ b/src/main/resources/config.yml
@@ -1,6 +1,9 @@
 # The URL of your Discourse installation (without the trailing slash)
 discourse-url: http://forum.example.com
 
+# Message to display if kicking due to whitelist
+kick-message: You are not on the whitelist
+
 # A mapping between Discourse groups (by integer ID) and Minecraft groups (by name)
 groups: