Facing a lawsuit by the U.S. Department of Justice, the parent companies of American Airlines and US Airways have agreed to extend their merger plans for an extra month.

The expiration date to merge the airlines to create the nation's largest airline has been moved from Dec. 17 to Jan. 18, AMR Corp. and US Airways Group announced in a joint statement.

A trial to hear the Justice Department's challenge to the merger is scheduled to begin Nov. 25 at a district court in Washington. AMR, which had filed for bankruptcy in 2011, had hoped the merger would allow the carrier to clear bankruptcy.