Business necessity is a defense to a claim of discrimination under the ADA.
If you find that the defendant’s application of standards, criteria, or policies have [the effect of screening out or otherwise denying a job or benefit to individuals with plaintiff's disability] [a disparate impact on individuals with plaintiff's disability], the defendant must prove, by a preponderance of the evidence, that the standard, criterion, or policy:
1. is uniformly applied;
2. is job-related;
3. is consistent with business necessity; and
4. cannot be met by a person with plaintiff's disability even with a reasonable accommodation.
If you find that each of the elements on which the plaintiff has the burden of proof has been proved, your verdict should be for the plaintiff, unless you also find that the defendant has proved this affirmative defense, in which event your verdict should be for the defendant.
See 42 U.S.C. § 12113(a) (describing defenses and terms) and 29 C.F.R. § 1630.15(b)
The Supreme Court has recognized that the “direct threat” affirmative defense (whether an employee poses a threat to others or to the employee himself or herself) is consistent with “business necessity” principles encompassed in the ADA (§ 12113) and the EEOC regulations (29 C.F.R. § 1630.15(b)(2) (2001). Chevron U.S.A., Inc. v. Echazabal, 536 U.S. 73, 76-77 (2002).