Overtaxed and unpaid air traffic controllers are resigning “every day” due to stress from the government shutdown.

“Controllers are resigning every day now because of the prolonged nature of the shutdown,” Nick Daniels, president of the National Air Traffic Controllers Association, told CNN.

“We hadn’t seen that before. And we’re also 400 controllers short—shorter than we were in the 2019 shutdown.”

Air traffic controllers are federal workers, which means they are part of the approximately 730,000 federal employees working without pay since the shutdown began on Oct. 1.

Daniels warned that the controllers who remain are stretched dangerously thin. Many are calling in sick due to burnout as they struggle to pay bills.

“They’re calling their employer and saying, ‘I have no gas today. I cannot pay for my child care. Can I bring my children to work?’” he said.

On Oct. 7, less than a week after the shutdown began, Transportation Secretary Sean Duffy noted that some air traffic controllers were already taking second jobs—a practice he discouraged. “I don’t want them delivering for DoorDash; I don’t want them driving Uber,” he said. “I want them coming to their facilities and controlling the airspace.”

The resignations are adding to the tremendous stress being placed on airports due to the government shutdown. Just this week, staffing shortages reached their highest levels since the shutdown began.

The Trump administration has responded to the crisis by curbing air traffic by 10 percent in 40 “high-traffic” markets, including New York City, Boston, Los Angeles, and other major American cities.

The resignations also mean Americans can’t expect things to instantly return to normal once the shutdown ends, which is bad news for the upcoming holiday season.