The U.S. will cut flight capacity by 10% at 40 high-volume markets across the country, though international routes will be spared, to alleviate pressure on air traffic controllers and the aviation system during what is now the longest government shutdown in history.

The changes will start November 7, Transportation Secretary Sean Duffy said during a press briefing alongside the leader of the Federal Aviation Administration, Bryan Bedford. The agency plans to release the markets impacted on November 6.

“The data will dictate what we do,” Duffy said. “If the data goes in the wrong direction, could you see additional restrictions? Yes.”

CBS News reported the list includes airports in New York, Los Angeles, Chicago, Atlanta, Dallas and Washington. It also names cargo-heavy facilities in Louisville, Kentucky; Memphis; Anchorage, Alaska; and Ontario, California.

The network didn’t identify the source of its report and said the list isn’t final.

The reductions are expected to be staggered, with U.S. carriers informed on the night of November 5 that they should plan to cut flight volumes by 4% on November 7 and 5% on November 8, according to people familiar with the matter, who asked not to be identified because they’re not authorized to speak publicly.

That will build to 10% sometime next week, and international flights won’t be affected, they said. However, the situation is fluid, and the plan could still change, the people said.

The announced plans, if they impact the top 40 airports in the U.S., could cut as many as 1,800 flights, data analytics company Cirium said.

United Airlines Holdings Inc. offered the first glimpse of how U.S. carriers may implement the directive. Chief Executive Officer Scott Kirby said it will focus reductions on regional and domestic mainline flights that don’t travel between its primary hubs. 

Duffy said the cuts were necessary to maintain air travel safety. Bedford added that he sees the FAA restricting space launches as well. 

The FAA has been forced to slow traffic at many airports in recent days due to rising controller staffing shortages since the government shutdown began on October 1. Air traffic controllers continue to work without pay, adding strain to an already stressful job.

President Donald Trump also weighed in on the staffing-related delays and cancellations. “They’re stranding thousands of travelers at the airports,” he said at the America Business Forum in Miami. “All because they want to return to the failed Biden policies.”

Trump’s comments and an earlier round table with airline executives were the latest rhetoric intended to ratchet up pressure on Democrats to forge a deal to end the shutdown.

Fatigue Builds

Controller absences have increased as the shutdown drags on. Duffy has said that normally staffing shortages cause about 5% of flight delays, but that number has been routinely higher over the last month — at times surpassing 50%.

“We are starting to see some evidence that fatigue is building in the system,” Bedford said during the press conference on November 5, pointing to voluntary safety disclosure reports the FAA receives from pilots. He said it was important for the agency to take action to prevent the situation from deteriorating further. 

Millions of passengers have grappled with flight cancellations and delays related to staffing since the shutdown started, Airlines for America, a trade group, has said.