Major airlines braced for a third day of government-mandated flight cuts Sunday after rising air traffic control staffing shortages snarled thousands of flights on Saturday.

The Federal Aviation Administration instructed airlines to cut 4% of daily flights starting on Friday at 40 major airports because of air traffic control safety concerns. The shutdown, which has reached a record 40 days, has led to shortages of air traffic controllers who, like other federal employees, have not been paid for weeks.

Reductions in flights are mandated to reach to 6% on Tuesday and then hit 10% by Friday.