Whenever an agency or court of any State or territory is in doubt whether the Board would assert jurisdiction over the parties in a proceeding pending before such agency or court, the agency or court may file a petition with the Board for an advisory opinion on whether the Board would decline to assert jurisdiction over the parties before the agency or the court (1) on the basis of its current standards, or (2) because the employing enterprise is not within the jurisdiction of the National Labor Relations Act.