WASHINGTON The Federal Aviation Administration (FAA) said Thursday it is considering subjecting high-volume charter flight operators to stricter regulations imposed on passenger airlines.

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 no more than 30 seats, are not subject to the same first officer training, mandatory pilot age 65 retirement or minimum rest periods as airline pilots. Passengers on those flights also do not need to undergo Transportation Security Administration screening. The number of charter flights has grown dramatically over the last decade.

The FAA said 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.

(Reporting by David Shepardson)