49 CFR §39.25

1. (a)As a PVO, you must not refuse to provide transportation or use of a vessel to a passenger with a disability on the basis of his or her disability, except as specifically permitted by this Part.
2. (b)You must not refuse to provide transportation or use of a vessel to a passenger with a disability because the person's disability results in appearance or involuntary behavior that may offend, annoy, or inconvenience crewmembers or other passengers.
3. (c)If you refuse to provide transportation or use of a vessel to a passenger on a basis relating to the individual's disability, you must provide to the person a written statement of the reason for the refusal. This statement must include the specific basis for your opinion that the refusal meets the standards of § 39.27 or is otherwise specifically permitted by this part. You must provide this written statement to the person within 10 calendar days of the refusal of transportation or use of the vessel.