A federal judge reinforced an order for American Airlines Group Inc. mechanics and other airport ramp workers to end an alleged work slowdown the carrier said has had a “devastating effect” on flights during the busy summer travel season.

U.S. District Judge John McBryde in Fort Worth, Texas, on Monday made permanent an earlier order directing the TWU-IAM Association to stop encouraging workers to delay aircraft repairs and other work and to reject overtime or out-of-town assignments.

“The concerted job action of defendants’ members has caused flight delays and cancellations, inconveniencing the public and disrupting commerce,” the judge wrote in a ruling.

American sued the union in late May, arguing it was using the slowdown to snarl operations during a critical travel period and to pressure the airline into a new contract agreement. More than 640 flights were canceled, affecting 88,000 passengers, during two months of the slowdown, and workers continued to cause major disruptions after McBryde’s initial order in June, the carrier said.

The union group denied the claims at a one-day trial on July 1, saying the airline couldn’t point to a specific flight that was canceled as a result of union activity or a single mechanic who had worked slowly. The TWU-IAM Association was created after the 2013 merger of American and US Airways to represent the Transport Workers Union of America and International Association of Machinists and Aerospace Workers in contract talks.

The association and the airline haven’t been able to agree on issues like compensation, health and retirement benefits and limits on outsourcing work in 3 1/2 years of negotiations. Talks were suspended April 25 by federal mediators because of a lack of progress.

The case is American Airlines Inc. v. Transport Workers Union of America, 19-cv-00414, U.S. District Court, Northern District of Texas (Fort Worth).