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.