U.S. airlines started cancelling hundreds of flights on Friday, hours after the Federal Aviation Administration ordered the cuts amid the more-than-month long government shutdown.

The cuts were ordered as air traffic controllers have missed their paychecks due to the government shutdown, now the longest in U.S. history. Air traffic control staffing shortages have been disrupting flights at several major U.S. airports, vexing travelers and airline executives alike.

More than 700 U.S. flights were canceled as of 9 a.m. ET Friday, according to aviation data firm Cirium, about 3% of the total schedule for the day. That scale of disruption is fairly common for routine disruptions like major thunderstorms, but the Department of Transportation warned that cancellations could ramp up.