Carriers who violated the directive could face fines of up to $75,000 per flight.

Zach Vasile

The FAA is investigating whether certain airlines violated its Nov. 7 order reducing flights at 40 of the nation’s busiest airports.

In a statement, the agency said it contacted carriers that operate more than 10 daily flights at any of the affected airports and is giving them 30 days to produce evidence that they complied with the flight reduction order. Airlines found to have violated the rule could face fines of up to $75,000 per flight that exceeded the emergency limits.

The FAA did not name any specific carriers, but the 10 daily flights criteria would include airlines like United, Delta, American, Southwest, and JetBlue, among others.

Agency officials said last month that they were looking into “reports of non-compliance by carriers,” but it was not clear at the time if a full-blown investigation would be launched.

The FAA began cutting flight traffic during the recent federal government shutdown to ease the burden on air traffic controllers working without a pay. The cuts – which targeted major airports such as Chicago O’Hare, Denver, Atlanta, Los Angeles, New York-JFK, and many more – resulted in thousands of canceled flights per day, in addition to thousands of delays.

Reductions started at 4%, rose to 6%, and were dropped entirely days after the federal government officially reopened.