Associated Press / news@whmi.com

Airports in Detroit, New York, Los Angeles and Chicago along with hubs across the U.S. are among the 40 that will see flights cut starting Friday due to the government shutdown, according to a list distributed to the airlines and obtained by The Associated Press.

The Federal Aviation Administration said Wednesday that it will reduce air traffic by 10% across 40 “high-volume” markets to maintain travel safety as air traffic controllers exhibit signs of strain during the ongoing government shutdown.

Air traffic controllers are working without pay during the government shutdown and have been increasingly calling off work.

Controllers already have missed one paycheck and are scheduled to again receive nothing next week as as the shutdown drags on and the financial pressure on them mounts.

The FAA has already been delaying flights at times when airports or its other facilities are short on controllers.

Passengers should start to be notified about cancellations Thursday. Airlines said they would try to minimize the impact on customers, some of whom will see weekend travel plans disrupted with little notice.

United Airlines said it would focus the cuts on smaller regional routes that use smaller planes like 737s. United, Delta Air Lines and American Airlines said they would offer refunds to passengers who opt not to fly — even if they purchased tickets that aren’t normally refundable.

The head of Frontier Airlines recommended travelers buy backup tickets with another airline to avoid being stranded.

Experts predict hundreds if not thousands of flights could be canceled. The cuts could represent as many as 1,800 flights and upwards of 268,000 seats combined, according to an estimate by aviation analytics firm Cirium.

“I’m not aware in my 35-year history in the aviation market where we’ve had a situation where we’re taking these kinds of measures,” FAA Administrator Bryan Bedford said Wednesday. “We’re in new territory in terms of government shutdowns.”

Mounting staffing pressures are forcing the agency to act, Bedford said.

“We can’t ignore it,” he said, adding that even if the shutdown ends before Friday, the FAA wouldn’t automatically resume normal operations until staffing improves and stabilizes.