Follow live updates as flight reductions begin today at 40 high-traffic airports in what officials have described as a "proactive" effort to alleviate pressure points.

The FAA released the list of affected airports Thursday, with a focus on areas that have been struggling most with air-traffic-control staffing shortages. The list includes some of the nation’s biggest, busiest airports, including those in Atlanta, Chicago, Dallas and New York City.

Airlines are canceling hundreds of flights to comply with the FAA's order. But there are still questions about the plan, which the agency says will keep the skies safe during the government shutdown.

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.

FAA told airlines to cut flight volume by 10% at 40 airports, including Minneapolis-St. Paul International Airport, amid government shutdown stalemate.

Federal officials say the mandatory FAA slowdown is necessary to maintain safe skies during the government shutdown.

Sara Nelson, president of the Association of Flight Attendants, joins Morning Joe as hundreds of flights are canceled amid the ongoing government shutdown, warning the system is “unsustainable” and that people “will break” if air traffic workers remain unpaid.

TSA wait times at George Bush Intercontinental Airport were expected to exceed 45 minutes to an hour, according to airport officials.