The Federal Aviation Administration said Wednesday that it would reduce air traffic by 10% across 40 “high-volume” markets beginning Friday morning to maintain safety during the ongoing government shutdown.

The reduction stands to impact thousands of flights nationwide because the FAA directs more than 44,000 flights daily, including commercial passenger flights, cargo planes and private aircraft.

Air traffic controllers have been working unpaid since the shutdown began Oct. 1. With some calling out of work, staffing shortages during some shifts have led to flight delays at a number of U.S. airports.

Citing growing staffing pressures, FAA Administrator Bryan Bedford said the agency would not wait for a crisis to act

“We can’t ignore it,” he said.

Bedford and Transportation Secretary Sean Duffy said they would meet with airline executives later Wednesday to determine how to safely implement the reduction in flights. Until then, both declined to name the affected markets. Bedford said a list would be released sometime Thursday.