U.S. Transportation Secretary Sean Duffy warned Friday he could force airlines to cut up to 20% of flights if the government shutdown did not end, as U.S. airlines on Friday scrambled to make unprecedented government-imposed reductions.

The Federal Aviation Administration instructed airlines to cut 4% of flights on Friday at 40 major airports because of the government shutdown. The cuts will rise to 10% by November 14.

Separately, air traffic controller absences on Friday forced the FAA to delay hundreds of flights at 10 airports including Atlanta, San Francisco, Houston, Phoenix, Washington, D.C., and Newark. By 7:30 p.m. ET (1130 GMT), there were more than 5,300 flight delays, according to FlightAware, a flight-tracking website.

At Reagan Washington National, delays were averaging fou

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