Definition of "undue burden" in section 36.104 of "ADA Title III Regulation 28 CFR Part 36" www.ada.gov/reg3a.html
Undue burden means significant difficulty or expense. In determining whether an action would result in an undue burden, factors to be considered include --
(1) The nature and cost of the action needed under this part;
(2) The overall financial resources of the site or sites involved in the action; the number of persons employed at the site; the effect on expenses and resources; legitimate safety requirements that are necessary for safe operation, including crime prevention measures; or the impact otherwise of the action upon the operation of the site;
(3) The geographic separateness, and the administrative or fiscal relationship of the site or sites in question to any parent corporation or entity;
(4) If applicable, the overall financial resources of any parent corporation or entity; the overall size of the parent corporation or entity with respect to the number of its employees; the number, type, and location of its facilities; and
(5) If applicable, the type of operation or operations of any parent corporation or entity, including the composition, structure, and functions of the workforce of the parent corporation or entity.