14 C.F.R. § 399.89
Any seller of scheduled air transportation within, to or from the United States, or of a tour (i.e., a combination of air transportation and ground or cruise accommodations), or tour component (e.g., a hotel stay) that includes scheduled air transportation within, to or from the United States, must notify a consumer of the potential for a price increase that could take place prior to the time that the full amount agreed upon has been paid by the consumer, including but not limited to an increase in the price of the seat, an increase in the price for the carriage of passenger baggage, an increase in an applicable fuel surcharge, or an increase in a government-imposed tax or fee and must obtain the consumer's written consent to the potential for such an increase prior to accepting any payment for the scheduled air transportation, or tour or tour component that includes scheduled air transportation. Imposition of any such increase without providing the consumer the appropriate notice and obtaining his or her written consent to the potential increase constitutes an unfair and deceptive practice within the meaning of 49 U.S.C. 41712 .
14 C.F.R. §399.89