The New York Transit Authority (D) refused to employ people who used narcotic drugs. D refused to hire Beazer (P) because he used the drug methadone to treat his heroin addiction. This litigation was brought by the four respondents as a class action on behalf of all persons who have been, or would in the future be, subject to discharge or rejection as employees of TA by reason of participation in a methadone maintenance program. Two of the respondents are former employees of D who were dismissed while they were receiving methadone treatment. The other two were refused employment by D, one both shortly before and shortly after the successful conclusion of his methadone treatment, and the other while he was taking methadone. Their complaint alleged that D's blanket exclusion of all former heroin addicts receiving methadone treatment was illegal under the Civil Rights Act of 1866 and the Equal Protection Clause of the Fourteenth Amendment. The trial court found that at least half of all methadone users were employable. The District Court enjoined D from denying employment to any person solely because of participation in a methadone maintenance program. Recognizing, however, the special responsibility for public safety borne by certain D employees and the correlation between longevity in a methadone maintenance program and performance capability, the injunction authorized D to exclude methadone users from specific categories of safety-sensitive positions and also to condition eligibility on satisfactory performance in a methadone program for at least a year. D could lawfully adopt general rules excluding all methadone users from some jobs and a large number of methadone users from all jobs. The court of appeals affirmed, and the Supreme Court granted certiorari.