The Federal Aviation Administration has warned Southwest Airlines and its mechanics union that their legal dispute could end up damaging the safety of the airline.
In a letter sent to the airline and the union on Friday, the agency’s top safety official, Ali Bahrami, said the dispute “raises concern about the ongoing effectiveness of the airline’s safety management system.”
Southwest sued the union on Feb. 28, claiming that a work slowdown had illegally grounded many of the airline’s planes and caused over 100 flight cancellations since the middle of the month. The lawsuit’s implication was that the union had grounded the planes to gain leverage in contract negotiations, which have been going on for years and had recently broken down over how much of the airline’s maintenance work would be outsourced.
The union, the Aircraft Mechanics Fraternal Association, said it had grounded the planes because of safety concerns.
In a statement, Southwest played down the importance of the letter from the federal agency. “This type of communication is normal protocol designed to underscore continued safe operations during such times at a carrier,” the statement said.
Bret Oestreich, the national director of the mechanics union, declined to comment on the letter, a copy of which was obtained by The New York Times.
It is not unusual for airlines and their unions to end up in court, but the Southwest dispute has been particularly heated. The airline also sued the union in 2017 over a conflict related to overtime pay, and that suit is still pending.
On Feb. 22, Southwest declared an operational emergency in a memo to the union, according to reports. The union responded with a public letter denying that the mechanics were improperly grounding aircraft.
In his letter on Friday, Mr. Bahrami said the F.A.A. was a neutral party in the legal dispute, but he cautioned that the airline and the union were both responsible for ensuring that the airline met the agency’s safety standards.
“Safety is a shared responsibility of Southwest and A.M.F.A. members that demands a collaborative culture,” he wrote, “irrespective of any ongoing controversy between the two organizations.”