Airline unions have opposed the expansion of charter operations. Association of Flight Attendants-CWA President Sara Nelson praised the FAA action, calling the charter regulations a "loophole that undermines safety and security rules for commercial aviation."

Charter flights, which can have a maximum of 30 seats, are not subject to the same training for first officers, mandatory retirement of pilots at age 65 or minimum rest periods for airline pilots. Passengers on those flights also need not be screened by the Transportation Security Administration.

The number of charter flights has grown dramatically over the last decade.

The FAA said on Thursday "this rapid growth poses an increased risk to safety if left unchecked" and said it will "begin a rulemaking to address this safety risk."

SkyWest has sought approval to conduct passenger operations through a separate charter operation and faces strong opposition from unions. The Transportation Department has not yet acted on the request.

SkyWest Charter said on Thursday it believes the charter designation "is essential for small community air service, today and well into the future." The air carrier added it "already exceeds current safety requirements and will transition to any additional requirements that may be adopted by the FAA as part of the rulemaking process."

Aviation unions and American Airlines have criticized growing charter operations by air carrier JSX. American said in May that JSX had a "competitive advantage" by operating under less stringent regulatory rules.

JSX had 110,000 departures in 2022 with its 37 aircraft - more than some small regional passenger airlines, unions argued.

JSX said on Thursday the FAA notice "is disappointing, both for the traveling public and for the advancement of vital air mobility programs around the nation ... JSX complies with all applicable rules and regulations and far exceeds the safety requirements germane to our public charter operations."

Dallas-based JSX counts both United Airlines and

JetBlue Airways as investors.

(Reporting by David Shepardson in WashingtonEditing by Matthew Lewis)

By David Shepardson