United Airlines has updated its contract of carriage to state that failure to use headphones while listening to audio or video content could be grounds for removing a passenger from a plane and banning them from future flights. The rule also includes an additional reason for which United may have the right to refuse transport on a permanent basis or remove passengers from the aircraft at any point. This move sets the stage for reciprocal moves across airlines and countries. The issue of speaker use on airplanes and public spaces has been a frequent complaint from disgruntled passengers, with some labeling it as "speaker scum".