There is a thing called Bona Fide Occupational Qualifications where an employer could discriminate against protected classes because the job description is so specific. Like if a church wanted to hire a new pastor, the job description requires the applicant to be Christian and likely a specific denomination, and any non-christian would be disqualified from the position. BFOQs must be spelled out in the job description to make it absolutely clear that the qualifications are necessary for the job. Also age, sex, and gender can be BFOQs like if the job description is for an acting role of a specific character. Race could potentially apply to something like an acting job too but that's a lot more of a dicey subject, like it would need to be absolutely critical to the production that a character is a specific race.