It depends on the situation: Employers can require documentation saying that the service animal is a fully trained service dog or miniature horse capable of being the workplace and is necessary to help the disabled person / employee. Airlines can require documentation of the medical or therapeutic necessity of flying with the animal. Landlords can ask the prospective lessee if the animal is necessary to live in the rental. Landlords can also ask for documentation attesting that the prospective lessee has a disability that has functional limitations. Otherwise, service providers or places of business are prohibited from requiring documentation that the animal is a service animal (or a service animal in training). Nor can these facilities ask about the service dog owner's disability or charge a fee to admit the assistance animal. All business owners can ask is if the animal is indeed a service animal, and what they are trained to do.