28 C.F.R. § 35.164
This subpart does not require a public entity to take any action that it can demonstrate would result in a fundamental alteration in the nature of a service, program, or activity or in undue financial and administrative burdens. In those circumstances where personnel of the public entity believe that the proposed action would fundamentally alter the service, program, or activity or would result in undue financial and administrative burdens, a public entity has the burden of proving that compliance with this subpart would result in such alteration or burdens. The decision that compliance would result in such alteration or burdens must be made by the head of the public entity or his or her designee after considering all resources available for use in the funding and operation of the service, program, or activity and must be accompanied by a written statement of the reasons for reaching that conclusion. If an action required to comply with this subpart would result in such an alteration or such burdens, a public entity shall take any other action that would not result in such an alteration or such burdens but would nevertheless ensure that, to the maximum extent possible, individuals with disabilities receive the benefits or services provided by the public entity.
28 C.F.R. § 35.164