US Airways and American Airlines are extending their merger deadline by a month to give themselves time for the antitrust trial scheduled for November.

That trial is scheduled to begin Nov. 25. Their original agreement allowed either side to call off the merger on Dec. 17, but the trial might not be done by then. The new agreement extends that period until Jan. 18, or later if the court rules in favor of the airlines.

The Justice Department has sued to stop the planned merger, saying it will hurt competition. The airlines have argued that other mergers were allowed to go forward, and that this merger is needed so they can compete with the new, larger United and Delta.