The Air Carrier Access Act of 1986 (ACAA) prohibits discrimination on the basis of disability in air travel by airlines that offer flights in the United States, and to and from the United States by foreign airlines.
The ACAA serves to protect the rights of passengers with disabilities, making it unlawful to refuse transportation because of disability, among other regulated practices. The Department of Transportation (DOT) rule under this law on passenger rights and prohibited practices is Title 14 CFR Part 382 (Nondiscrimination on the Basis of Disability in Air Travel).
§382.11 provides the following list of general practices you must not do as a carrier:
You must not discriminate against any qualified individual with a disability, by reason of such disability, in the provision of air transportation;
You must not require a qualified individual with a disability to accept special services (including, but not limited to, preboarding) that the individual does not request. However, you may require preboarding as a condition of receiving certain seating or in-cabin stowage accommodations, as specified in §§382.83(c), 382.85(b), and 382.123(a) of this part.
You must not exclude a qualified individual with a disability from or deny the person the benefit of any air transportation or related services that are available to other persons, except where specifically permitted by this Part. This is true even if there are separate or different services available for individuals with a disability, except when specifically permitted by another section of this Part; and
You must not take any adverse action against an individual (e.g., refusing to provide transportation) because the individual asserts, on his or her own behalf or through or on behalf of others, rights protected by this part or the Air Carrier Access Act.
The DOT File a Consumer Complaint page advises that before you contact the DOT for help, you should try to work with the airline first. Airlines are required to acknowledge complaints within 30 days and provide a written response within 60 days.
If you still would like to file a complaint with the DOT or if you believe you may have been discriminated against unlawfully, you may file a complaint by following the information on the DOT File a Consumer Complaint page, calling the DOT by phone at 202-366-2220 (TTY 202-366-0511), or by mail:
Aviation Consumer Protection Division, C-75
U.S. Department of Transportation
1200 New Jersey Avenue, SE
Washington, DC 20590