An employer faced with an allegation of discrimination resulting from disparate impact can defend against the allegation by claiming business necessity. To use this defense, the employer must prove that there was a real business purpose behind the workplace practice or policy that resulted in discrimination. There must also be no other way to achieve the same business purpose without having a discriminatory impact. This defense does not exist for employers facing claims of disparate treatment.
See, CACI 2503 and City and County of San Francisco v. Fair Employment and Housing Com. (1987) 191 Cal.App.3d 976, 989-990.