WASHINGTON (AP) — Air traffic in the U.S. could “slow to a trickle” if the federal government shutdown lingers into the busy Thanksgiving travel holiday season, Transportation Secretary Sean Duffy warned Sunday.

The Federal Aviation Administration last week ordered flight cuts at the nation’s busiest airports as some air traffic controllers, who have gone unpaid for nearly a month, have stopped showing up for work.

The reductions started Friday at 4% and will increase to 10% by Nov. 14. They are in effect from 6 a.m. to 10 p.m. local time and will impact all commercial airlines.

On Sunday, 1,375 flights were canceled as of 10:30 a.m. Eastern time, according to the aviation tracking website FlightAware. That follows more than 1,500 cancellations on Saturday.

Duffy has said additional flight cuts — perhaps up to 20% — might be needed, particularly after controllers receive no pay for a second straight pay period.

“More controllers aren’t coming to work day by day, the further they go without a paycheck,” Duffy told “Fox News Sunday.”

And he prepared Americans for what they could face during the busy Thanksgiving holiday.

“As I look two weeks out, as we get closer to Thanksgiving travel, I think what’s going to happen is you’re going to have air travel slow to a trickle as everyone wants to travel to see their families,” Duffy said.

With “very few” controllers working, “you’ll have a few flights taking off and landing” and thousands of cancellations, he said.

“You’re going to have massive disruption. I think a lot of angry Americans. I think we have to be honest about where this is going. It doesn’t get better,” Duffy said. “It gets worse until these air traffic controllers are going to be paid.”

The government has been short of air traffic controllers for years, and multiple presidential administrations have tried to convince retirement-age controllers to remain on the job. Duffy said the shutdown has exacerbated the problem, leading some air traffic controllers to speed up their retirements.

“Up to 15 or 20 a day are retiring,” Duffy said on CNN.

Duffy said Defense Secretary Pete Hegseth texted him with an offer to lend military air traffic controllers, but it’s unclear whether the staff is certified to work on civilian systems.

Duffy denied Democratic charges that the flight cancellations are a political tactic, saying they were necessary due to increasing near-misses from an overtaxed system.

“I needed to take action to keep people safe,” Duffy said. “I’m doing what I can in a mess that Democrats have put in my lap.”