Title VII of the Civil Rights Act of 1964 prohibits discrimination based on sex and other criteria. But there are some defenses to discrimination. One of these is the "BFOQ" or bona fide occupational qualification.
As the court of appeals explained in Breiner v. Nevada Dept. of Corrections, the BFOQ defense is "an 'extremely narrow exception to the general prohibition of discrimination on the basis of sex' that may be invoked 'only when the essence of the business operation would be undermined' by hiring individuals of both sexes."
So, the Nevada prison system was beset by a number of instances of male corrections officers engaging in sexual conduct with female inmates. A guard impregnated an inmate, which came to the attention of administration. The inmates purposely traded favors for better treatment.
Nevada's response, in part, was to exclude males from certain jobs, including "Corrections Lieutenant" at women's prisons. The thought was that hiring only female lieutenants would cut down corruption caused by female inmates' solicitations. Some male corrections officers sued, saying they were denied promotional opportunities at the female prisons.
The Ninth Circuit reversed the prison systems' summary judgment victory. The court did not believe that Nevada adequately supported its justification for discriminating against male candidates for hiring at women's prisons.
This opinion explains in detail the BFOQ defense and the employer's difficulty proving it. Much of the opinion focuses on prison cases, but the BFOQ defense and its burdens will be applicable to all businesses seeking to establish a sufficient justification for hiring women or men exclusively in a particular setting.
The case is Breiner v. Department of Corrections and the opinion is here.