49 CFR Part 37 - Transportation for Individuals With Disabilities; Reasonable Modification of Policies and Practices

(h) It is not discrimination under this part for an entity to refuse to provide service to an individual with disabilities because that individual engages in violent, seriously disruptive, or illegal conduct, or represents a direct threat to the health or safety of others. However, an entity shall not refuse to provide service to an individual with disabilities solely because the individual's disability results in appearance or involuntary behavior that may offend, annoy, or inconvenience employees of the entity or other persons.