John Becker, of Silver Spring, waves a rainbow flag last June in anticipation of a ruling on gay marriage from the Supreme Court. (Photo by Bill O'Leary/The Washington Post)

The gay rights movement has made a lot of progress at the Supreme Court in the past few years, with decisions tossing out the federal Defense of Marriage Act and then legalizing same-sex marriage altogether. But one big piece of the puzzle is still missing: a ruling on the question of whether gay men and lesbians are protected against discrimination in the workplace.

The person who replaces Justice Antonin Scalia on the bench could decide the matter for good.

Gay rights advocates have long argued that Title VII of the Civil Rights Act of 1964, by prohibiting discrimination on the basis of sex, also extends to discrimination on the basis of sexual orientation. Over the past few years, the Equal Employment Opportunity Commission has agreed, issuing a series of complaints and amicus briefs charging employers for violating the rights of gay, lesbian  and transgender workers.

A couple of weeks ago, the Justice Department also seemed to take that position, when it allowed a complaint of sexual orientation discrimination to move forward rather than dismiss it outright.

“In the past there has been a general understanding that sexual orientation wasn’t illegal under federal law,” says Paul Smith, a lawyer at Jenner & Block who has argued some of the nation’s most significant gay rights cases. “And this one time, [the Justice Department] stopped making an argument. So that’s been interpreted as a change in policy.” The Justice Department did not respond to a request to clarify its intention.

The issue is likely to wind up at the Supreme Court. So far, district courts have issued rulings in both directions, and cases are pending at the U.S. Courts of Appeals for the 7th and 11th circuits. The high court tends to step in when appellate courts start disagreeing with each other, which could happen within the next couple of years.

At this point, it’s hard to tell which suit will go all the way to the Supreme Court. Employers often settle these cases, agreeing to remedy the problem and make the parties whole rather than have their name associated with a decision that stands in the way of equal rights for gay men and lesbians at a time of rapidly rising acceptance.

Right now, the plaintiff in one of those cases — against Walmart, which didn’t offer health insurance to their employees’ same-sex spouses until 2014 — has more immediate concerns.

Last year, a Massachusetts Walmart employee of 15 years named Jacqueline Cote sued the company for the cost of caring for her wife, Diana Smithson. Smithson had also worked for Walmart but stopped in 2008 to care for Cote’s dementia-stricken mother. Then, in 2012, Smithson developed ovarian cancer.

Cote had assumed Walmart’s health insurance policy would cover the two of them. But Smithson was denied, and the couple racked up hundreds of thousands of dollars in medical bills before Walmart changed its policy after the Supreme Court’s 2013 decision in United States v. Windsor deeming same-sex marriages to be equal to heterosexual ones.

Now, Smithson is in the late stages of cancer, already past the time doctors had estimated she would live. “It’s been a rough go,” Cote says. Her wife may not survive to see a resolution to the case but would like to be able to pay her hospital bills. “That’s her biggest issue right now, the fact that we weren’t able to pay those doctors and nurses in the hospital for all the treatment she received,” Cote says.

Last week, a notice seeking others affected by Walmart's actions went out to the 1,200 current and former employees who enrolled a same-sex spouse in retailer's health plan after Jan. 1, 2014. The class action argues that, because the Civil Rights Act prohibits discrimination on the basis of sex, they should have been receiving benefits even before the Supreme Court invalidated the Defense of Marriage Act.

“We’re not just saying, ‘Let’s everyone move forward because it’s not happening anymore.’ These people were harmed, and should get justice,” says Peter Romer-Friedman, deputy legal director of the Washington Lawyers Committee for Civil Rights and Urban Affairs, which is helping with the case. “If Walmart tries to use [the Defense of Marriage Act] as a shield, I think they’re barking up the wrong tree. Because in light of what the Supreme Court did in Windsor, DOMA never existed.”

Walmart declined to comment on the ongoing litigation. It’s certainly possible, however, that the company will settle the case, leaving the legal arguments unresolved.

Of course, Congress has the power to cut this process short, by passing a law banning discrimination on the basis of sexual orientation. Sen. Jeff Merkley (D-Ore.) has introduced a more expansive version of the perennial Employee Non-Discrimination Act, but its prospects in a Republican-led Congress are not great.

“Winning some cases on the marriage equality front built an inevitability narrative, and that could help with the legislation in this context as well,” says Greg Nevins, an attorney with Lambda Legal, a national organization fighting for the civil rights of lesbians, gay men, bisexuals, transgender people and those with HIV. But if Congress doesn’t budge, he thinks the high court will eventually affirm that gay men and lesbians are protected under current law — at least, if Scalia’s replacement sees things the same way.

“In that sense, we would want someone who wouldn’t bring a negative, anti-gay agenda,” Nevins says. “But for this purpose, someone who just agrees that Title VII should be interpreted according to its words would help our cause.”