28 CFR Part 36 Nondiscrimination on the Basis of Disability by Public Accommodations and in Commercial Facilities NPRM (2008 Title III NPRM)

(ii) The type of auxiliary aid or service necessary to ensure effective communication will vary in accordance with the method of communication used by the individual, the nature, length, and complexity of the communication involved, and the context in which the communication is taking place.  A public accommodation should consult with individuals with disabilities whenever possible to determine what type of auxiliary aid is needed to ensure effective communication, but the ultimate decision as to what measures to take rests with the public accommodation, provided that the method chosen results in effective communication.