American Airlines said that the 4% reduction will mean 220 canceled flights per day. The vast majority of impacted American Airlines flights are regional, and there’ll be no impact to international flights including Mexico, Canada and the Caribbean, CEO David Seymour said in a letter to employees. Further hub-to-hub routes impact will be minimized.

The Federal Aviation Administration has announced a 10% reduction in flight capacity across 40 major U.S. airports.

San Francisco International Airport was among the major U.S. air-travel hubs to face cancellations as the federal government places limits on air travel.

While not all of the canceled flights were caused by the FAA-mandated cuts, airlines have reported cutting hundreds of flights due to the order.

Transportation Secretary Sean Duffy warned as many as 20% of flights could be canceled if the government shutdown drags on.

Air traffic controllers, along with airport security screeners, are required to work during the shutdown without receiving their regular paychecks. Federal workers will miss their second full paycheck on Monday, according to their union. Some controllers have taken second jobs to make ends meet, union officials have said.

The FAA is ordering airlines to cut thousands of flights nationwide, as cities deal with a severe shortage of air traffic controllers during the government shutdown.

The FAA will reduce air traffic at 40 airports beginning Friday. Philadelphia International Airport is among those expecting flight cuts and delays. Talks between Democrats and Republicans to end the shutdown are intensifying,