24 C.F.R. § 8.33
A recipient shall modify its housing policies and practices to ensure that these policies and practices do not discriminate, on the basis of handicap, against a qualified individual with handicaps. The recipient may not impose upon individuals with handicaps other policies, such as the prohibition of assistive devices, auxiliary alarms, or guides in housing facilities, that have the effect of limiting the participation of tenants with handicaps in the recipient's federally assisted housing program or activity in violation of this part. Housing policies that the recipient can demonstrate are essential to the housing program or activity will not be regarded as discriminatory within the meaning of this section if modifications to them would result in a fundamental alteration in the nature of the program or activity or undue financial and administrative burdens.
24 C.F.R. § 8.33