public function unlabel($userId, $opts = array()) {
        $this->mergeArguments($opts, array(
            'abuse_type' => null,
            'timeout' => $this->timeout,
            'version' => $this->version
        ));

        $this->validateArgument($userId, 'user id', 'string');

        $params = array('api_key' => $this->api_key);
        if ($opts['abuse_type']) $params['abuse_type'] = $opts['abuse_type'];

        try {
            $request = new SiftRequest(self::userLabelApiUrl($userId, $opts['version']),
                SiftRequest::DELETE, $opts['timeout'], $opts['version'], array('params' => $params));
            return $request->send();
        } catch (Exception $e) {
            $this->logError($e->getMessage());
            return null;
        }
    }