I believe carriers have some latitude in this area.
Because the rulemaking process will undoubtedly take time, until it is completed the Office of the Assistant General Counsel for Aviation Enforcement and Proceedings as a matter of prosecutorial discretion will not enforce the requirement that carriers freeze the price of ancillary services and products not purchased with the ticket (with the exception of any fees for carry-on bags and the first and second checked bags) for a given consumer at the time that he or she purchases the air transportation.
https://www.transportation.gov/sites...20Dec%2028.pdf