49 CFR §39.43

1. (a)As a PVO, you must not charge higher fares, surcharges, or other fees to passengers with a disability that are not imposed on other passengers for transportation or use of the vessel.
2. (b)If the accommodations on a vessel that are accessible to passengers with a disability are available only in a type or class of service or part of a vessel that are more expensive than the type or class of service or part of a vessel that the passenger requests, you must provide the accessible accommodation at the price of the type or class of service or facility that the passenger requests.
3. (c)You must not impose special or extra charges for providing facilities, equipment, or services that this rule requires to be provided to passengers with a disability.