American Airlines and JetBlue Airways on Monday asked a U.S. judge to dismiss a lawsuit that the Justice Department and six states filed over the carriers’ partnership in the Northeast.

The lawsuit, filed in federal court in Massachusetts in September, alleges that the airlines’ so-called Northeast Partnership, violates antitrust law, would reduce competition in the region and could drive up airfares and lower service quality.

That partnership lets American and JetBlue sell each other’s flights to and from the Northeast U.S., including usually congested airports in Boston and the New York City area. The airlines had argued that the partnership, approved at the end of the Trump administration, would allow them to better compete against Delta Air Lines and United Airlines in the region.

American and JetBlue said Monday that the Justice Department and other plaintiffs haven’t shown that the alliance has hurt competition or driven up fares and as a result the lawsuit should be tossed.

“The NEA has been underway for nine months, yet Plaintiffs do not allege that it has caused a single higher price, any reduction in quality or the slightest reduction in output,” the airlines wrote.

The Justice Department declined to comment.