When can a provider deny a request? - The Network
Category: reasonable accommodation faq

A housing provider can deny a request if it was not made by (or on behalf of) you, if you don’t have a disability-related need for the request, or if the request would be an “undue financial and administrative burden” for the housing provider. 

Whether a request causes an “undue burden” is decided case-by-case, based on factors such as cost, the housing provider’s resources, the benefits of the accommodation, and the availability of alternate ways to meet your needs.