Does a 50-year-old law banning discrimination based on sex mean employers must treat biological men who identify as women as if they are women? That’s the question the Supreme Court will consider Tuesday when it hears arguments in Harris Funeral Homes v. Equal Employment Opportunity Commission.

The Supremes’ answer could have enormous implications for women’s rights.

Harris Funeral Homes has helped families in Detroit navigate the grieving process for more than a century. To be as unobtrusive as possible, the directors at this family-owned business follow a basic dress code: Men wear dark business suits; women wear skirt suits. The dress code complies with federal law.

For six years, Anthony Stephens followed it. Then he ­announced that he would take a two-week vacation and returned to work dressed as a woman ­going by the name Aimee.

The owners faced a dilemma: They cared about Stephens; they also cared about the grieving families they served. They had concerns about how Stephens’ dressing as a woman would affect clients’ grieving. Also problematic were the funeral home’s single-sex bathrooms: Should they make female ­employees and guests share a bathroom with Stephens?

Ultimately they decided to let Stephens go. Then they got sued for sex discrimination.

The Equal Employment Opportunity Commission during the Obama years sided with Stephens. President Trump’s Department of Justice has supported the funeral home. Team Trump has the better legal argument.

The Civil Rights Act of 1964 bans employment discrimination because of sex. That means no double standards for men and women: You can’t have a funeral home that hires only men as ­funeral directors and women as morticians; you can’t have an ­accounting firm that promotes aggressive men for being manly but punishes aggressive women for being “unladylike.”

While the Civil Rights Act bans these double standards, it requires “neither asexuality nor androgyny,” as a unanimous high court ruled in a 1998 case.

That’s why bans on sex discrimination didn’t abolish sex-specific private facilities (like bathrooms), sex-specific fitness standards (for police and firefighters) or sex-specific athletic competitions (like the NBA and WNBA). After all, sex-specific bathrooms, fitness standards and sports leagues don’t disfavor men or women. On the contrary, they prevent disadvantageous treatment.

Forcing women to undress in locker rooms with men or to compete athletically against competitors with male muscle mass and stamina wouldn’t respect equality but undermine it.

Justice Ruth Bader Ginsburg took this point for granted when she wrote the high court’s majority opinion instructing the all-male Virginia Military Institute to become co-ed. She noted that going co-ed “would undoubtedly require alterations necessary to afford members of each sex privacy from the other sex in living arrangements.”

Excluding women from VMI, Ginsburg argued, discriminated on the basis of sex. Keeping men out of women’s private facilities, however, didn’t. This shouldn’t be controversial.

The Obama administration ­attempted to turn all of this upside down by claiming the word “sex” in our civil rights laws was determined by someone’s subjective “gender identity.” It’s an odd legal argument, given that the public meaning of the word “sex” — in 1964 and still today — refers to objective biological reality, not subjective identity.

Liberal activists have tried for years to get Congress to add “gender identity” as a protected class. Having failed, they took their arguments to unaccountable bureaucrats and activist judges. They failed with the bureaucrats, until Team Obama came around. And they failed in the courts — until March 2018, when a federal circuit court held that the Civil Rights Act banned discrimination based on transgender status.

Activists want the Supreme Court to affirm this novel ruling. To do so, the court would have to rewrite the law, thus usurping Congress’ role.

People who identify as transgender should be treated with dignity and respect. Whenever possible, we should make them feel comfortable. But the price of that accommodation can’t be the erasure of girls and women. It can’t be a law that requires businesses to allow males into female-only spaces — or that requires schools to allow boys who identify as girls into the girls’ locker room or onto their athletic teams.

Thankfully, the Civil Rights Act doesn’t require any of this. The Supreme Court shouldn’t rewrite our nation’s civil-rights laws in a way that would directly undermine one of their main purposes: protecting the equal rights of girls and women.

Biology isn’t bigotry.