Index: src/bp-activity/bp-activity-template.php
===================================================================
--- src/bp-activity/bp-activity-template.php
+++ src/bp-activity/bp-activity-template.php
@@ -2946,7 +2946,7 @@
 	 * @since 1.5.0
 	 *
 	 * @param bool   $can_comment Status on if activity reply can be commented on.
-	 * @param string $comment     Current comment being checked on.
+	 * @param object $comment     Current comment object being checked on.
 	 */
 	return (bool) apply_filters( 'bp_activity_can_comment_reply', $can_comment, $comment );
 }
Index: src/bp-groups/bp-groups-activity.php
===================================================================
--- src/bp-groups/bp-groups-activity.php
+++ src/bp-groups/bp-groups-activity.php
@@ -357,6 +357,75 @@
 	return bp_activity_add( $r );
 }
 
+/**
+ * Function used to determine if a user can comment on a group activity item.
+ *
+ * Used as a filter callback to 'bp_activity_can_comment'.
+ *
+ * @since 3.0.0
+ *
+ * @param  bool                      $retval   True if item can receive comments.
+ * @param  null|BP_Activity_Activity $activity Null by default. Pass an activity object to check against that instead.
+ * @return bool
+ */
+function bp_groups_filter_activity_can_comment( $retval, $activity = null ) {
+	// Bail if item cannot receive comments or if no current user.
+	if ( empty( $retval ) || ! is_user_logged_in() ) {
+		return $retval;
+	}
+
+	// Use passed activity object, if available.
+	if ( is_a( $activity, 'BP_Activity_Activity' ) ) {
+		$component = $activity->component;
+		$group_id  = $activity->item_id;
+
+	// Use activity info from current activity item in the loop.
+	} else {
+		$component = bp_get_activity_object_name();
+		$group_id  = bp_get_activity_item_id();
+	}
+
+	// If not a group activity item, bail.
+	if ( 'groups' !== $component ) {
+		return $retval;
+	}
+
+	// If current user is not a group member or is banned, user cannot comment.
+	if ( ! bp_current_user_can( 'bp_moderate' ) &&
+		( ! groups_is_user_member( bp_loggedin_user_id(), $group_id ) || ! groups_is_user_banned( bp_loggedin_user_id(), $group_id ) )
+	) {
+		$retval = false;
+	}
+
+	return $retval;
+}
+add_filter( 'bp_activity_can_comment', 'bp_groups_filter_activity_can_comment', 99, 1 );
+
+/**
+ * Function used to determine if a user can reply on a group activity comment.
+ *
+ * Used as a filter callback to 'bp_activity_can_comment_reply'.
+ *
+ * @since 3.0.0
+ *
+ * @param  bool        $retval  True if activity comment can be replied to.
+ * @param  object|bool $comment Current activity comment object. If empty, parameter is boolean false.
+ * @return bool
+ */
+function bp_groups_filter_activity_can_comment_reply( $retval, $comment ) {
+	// Bail if no current user, if comment is empty or if retval is already empty.
+	if ( ! is_user_logged_in() || empty( $comment ) || empty( $retval ) ) {
+		return $retval;
+	}
+
+	// Grab parent activity item.
+	$parent = new BP_Activity_Activity( $comment->item_id );
+
+	// Check to see if user can reply to parent group activity item.
+	return bp_groups_filter_activity_can_comment( $retval, $parent );
+}
+add_filter( 'bp_activity_can_comment_reply', 'bp_groups_filter_activity_can_comment_reply', 99, 2 );
+
 /**
  * Update the last_activity meta value for a given group.
  *