Section 399.88 - Prohibition on post-purchase price increase(a) It is an unfair and deceptive practice within the meaning of 49 U.S.C. 41712 for 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, to increase the ticket price of that air transportation, tour or tour component, or to raise the price for critical ancillary services as defined in § 399.85(a) to a consumer after the air transportation has been purchased by the consumer, except in the case of an increase in a government-imposed tax or fee. A purchase is deemed to have occurred when the full amount agreed upon has been paid by the consumer.(b) A seller of scheduled air transportation within, to or from the United States or 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 post-purchase price increase due to 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 purchase of the scheduled air transportation, tour or tour component that includes scheduled air transportation. Imposition of any such increase without providing the consumer the appropriate notice and without obtaining his or her written consent of the potential increase constitutes an unfair and deceptive practice within the meaning of 49 U.S.C. 41712 .Doc. No. DOT-OST-2010-0140, 76 FR 23167 , Apr. 25, 2011