28 C.F.R. § 35.204
Where a public entity can demonstrate that compliance with the requirements of § 35.200 would result in a fundamental alteration in the nature of a service, program, or activity or in undue financial and administrative burdens, compliance with § 35.200 is required to the extent that it does not result in a fundamental alteration or 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 § 35.200 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 a public entity or their 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 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 individuals with disabilities receive the benefits or services provided by the public entity to the maximum extent possible.
28 C.F.R. §35.204