https://www.hud.gov/program_offices/fair_housing_equal_opp/reasonable_accommodations_and_modifications
The Fair Housing Act
Under the Fair Housing Act a reasonable accommodation is a change, exception, or adjustment to a rule, policy, practice, or service. The Fair Housing Act makes it unlawful to refuse to make reasonable accommodations to rules, policies, practices, or services when such accommodations may be necessary to afford persons with disabilities an equal opportunity to use and enjoy a dwelling and public and common use areas.
In addition, the Fair Housing Act prohibits a housing provider from refusing to permit, at the expense of the person with a disability, reasonable modifications of existing premises occupied or to be occupied by such person if such modifications may be necessary to afford such person full enjoyment of the premises.