U.S. airlines are seeking another year of voluntary flight reductions at some of the nation’s most congested airports as the industry struggles with an ongoing shortage of air traffic controllers.

If federal aviation regulators grant the request, airlines could reduce flights at all three major New York City-area airports as well as Ronald Reagan Washington National until October 2025 without the risk of losing their valuable airport flight slots. Currently, the program is scheduled to expire this October.

Airlines for America, the trade group for major carriers, requested in a letter to the U.S. Transportation Department and the Federal Aviation Administration.

The flight reductions, first put in place in May 2023, followed a dramatic upswing in delays and cancellations as traffic surged back after the pandemic at the same time the U.S. was hit by a wave of controller retirements. Air traffic in the northeastern U.S. is particularly critical because disruptions there can easily cause a domino effect across the entire U.S. airspace.

“We still have a shortage of air traffic controllers, so it’s still an incredibly challenging environment,” Peter Carter, Delta Air Lines Inc.’s executive vice president of external affairs, said on a conference call Wednesday. “Absent the waivers, I think we’d have some real challenges as an industry in New York.”

Delta, American Airlines Group Inc., United Airlines Holdings Inc. and JetBlue Airways Corp. are among the carriers affected by the decision.

While some progress was made in increasing the FAA workforce last year, current and future staffing levels are “neither adequate to give consumers the travel experience they deserve, nor are they able to maximize the efficiency of the New York City airspace,” A4A, as the group is known, said in the letter. “Inadequate staffing will remain an immediate critical impediment” for the area during the 2024 winter season and 2025 summer season, the trade group said.

The flight limits helped improve on-time arrivals and departures at the participating airports in the fourth quarter, A4A said, as well as the percentage of flights completed.

Carriers have in some cases maintained capacity despite operating a lower volume of flights by using larger planes. As part of the plan, the FAA has been waiving the requirement for carriers to use the flight slots or lose them.