WASHINGTON (Reuters) -The Federal Aviation Administration on Thursday was working to hammer out details of an unprecedented plan to cut 10% of flights at 40 high-traffic U.S. airports to address safety concerns regarding air traffic controllers amid a record-setting federal government shutdown.

FAA Administrator Bryan Bedford told CEOs of major airlines late Wednesday the cuts would begin with 4% on Friday before rising to 10% next week.

The plan would exempt international flights and the cuts would apply to flights between 6 a.m. and 10 p.m. Airlines are seeking details about how to cancel flights. The FAA is also imposing drastic restrictions on space launches and general aviation.