D.C. Mun. Regs. tit. 4, r. 4-520
An employer may observe the conditions of a bona fide seniority system or a bona fide employee benefit system such as a retirement, pension, or insurance plan which is not a subterfuge to evade the purposes of Title I of the Act; provided, that no employee seniority system or benefit plan shall excuse the failure to hire any individual.
An employer may hire and employ employees on the basis of their membership in a class protected by Title I of the Act in special instances where sex, national origin, religion, disability, or other protected status is a business necessity for the normal operation of the particular business or enterprise.
Any religious or political organization, or any organization for charitable or educational purposes which is operated, supervised, or controlled by, or is operated in connection with, a religious or political organization may limit employment or give preferences to persons of the same religion or political persuasion as is calculated by such organization to promote the religious or political principles for which it is established or maintained.
Any practice which has a discriminatory effect and which would otherwise be prohibited by Title I of the Act shall not be deemed unlawful if it can be established that:
For purposes of this chapter, a "business necessity" exception shall be applicable only in the individual case where it can be proved that, without such exception, the business cannot be conducted. A "business necessity" exception shall not be justified by the factors of increased cost to business, business efficiency, the comparative characteristics of one group as opposed to another, the stereotyped characterization of one group as opposed to another, and the preferences of co-workers, customers, or any other persons.
D.C. Mun. Regs. tit. 4, r. 4-520