14 CFR §260.3

This part applies to: covered carriers that are the merchants of record; covered carriers that operate the flight or, for multiple-carrier itineraries, covered carriers that operate the last segment of a flight where a ticket agent is the merchant of record for a checked bag fee; and covered carriers that fail to provide an ancillary service (other than checked bag service) for which the consumer paid where a ticket agent is the merchant of record for an ancillary service fee other than checked bag fee.