WASHINGTON – Don Zarda was a daredevil. A New York skydiving instructor who lived to fly, he was fired from his job in 2010 after telling a female customer not to worry about being strapped tightly together because he was gay.

Zarda died in a risky BASE jumping accident in 2014, but his intrepid nature lives on in a daring legal dispute over his termination that will be heard Tuesday by the Supreme Court.

Together with a fired child welfare services coordinator from Georgia, Zarda – represented by his sister, Melissa, and former partner, Bill Moore – contends that a 1964 federal civil rights law barring sex discrimination in the workplace should include sexual orientation. In a related case, a fired funeral home worker from Michigan who is transgender says the statute should extend to gender identity.

"Nobody should be fired ever for being who they are," Melissa Zarda says. “I want the Supreme Court to stand by the fact that LGBT people are protected at work.”

The three cases are among the most significant on the high court's 2019 docket, and the justices' rulings are likely to come in the heat of the 2020 presidential campaign.

The challenges pick up where the same-sex marriage battle left off in 2015, when the court ruled 5-4 that states cannot ban gay men or lesbians from getting married.

More:Ex-funeral home worker’s case going to Supreme Court

"This is a more fundamental freedom than what was at stake in Obergefell," the same-sex marriage case won by James Obergefell and other LGBT plaintiffs, says Ria Tabacco Mar of the American Civil Liberties Union.

The challenge may be more difficult, however, for two reasons. The author of the high court's four major opinions expanding gay rights, Anthony Kennedy, retired last year and was succeeded by conservative Associate Justice Brett Kavanaugh. And rather than claiming a constitutional right, the challengers must convince at least five justices that the word "sex" in the Civil Rights Act of 1964 incorporates sexual orientation and gender identity.

How the court rules may come down to the comparison justices make. In court papers, lawyers for Zarda argue that "the relevant question ... is whether men who are attracted to men are being treated differently from women who are attracted to men."

The Trump administration, which lined up with the employers even though the Equal Employment Opportunity Commission had been on the other side, offers a different comparison "between a female employee in a same-sex relationship and a male employee in a same-sex relationship."

"They would be similarly situated," Solicitor General Noel Francisco argues in court papers, "and they would be treated the same."

'A nationwide issue'

Melissa Zarda remembers her big brother as brilliant, someone who seemed born to be an engineer.

“Normal kids would be playing with toys, and my brother would be wiring little circuit boards,” she recalls from her home in Kansas City.

When he decided to try his hand at skydiving, he called the night before near tears. The next day, after the jump, "he was a changed person," Melissa Zarda says. "Everything changed from that moment on."

Zarda was working for Altitude Express in Long Island, New York, in 2010 when he was accused of touching a female client inappropriately during a tandem jump. The company, which has since gone out of business, cited "a history of complaints against him" in court papers.

"He was devastated when he lost his job," Melissa Zarda says. "It was a crushing blow to him, and he knew that he needed to pursue it and try to right this wrong."

But as the legal case dragged on, Zarda had trouble finding work and took to BASE jumping from bridges and cliffs – "any way he could still enjoy skydiving and being in the air," his sister says. The risky sport eventually ended in his death at age 44, leaving Melissa Zarda and his partner at the time, Bill Moore, as executors of his estate – and plaintiffs before the Supreme Court.

Gerald Bostock's passion for protecting children began in southern Georgia, where he learned the values of faith, family and Friday night football.

As a child welfare services coordinator in Clayton County, he managed a program that provides court-appointed special advocates for children caught up in the court system. His goal, he says, was simple: "I did not want any child to fall through the cracks on my watch."

"It was my dream job, and I did my job well," Bostock says. "And then one day, I decided to join a gay recreational softball league, and that's when my life changed." He was fired several weeks later.

"They ruined my reputation within the child welfare industry, and that was a career for me, working with children," says Bostock, now 55. "I couldn't even get an interview." Instead, he landed a job as a mental health counselor at Georgia Regional Hospital.

"It’s no longer just about me," he says. "This is a nationwide issue that needs to be confronted. It impacts millions and millions of people across this country."

Dress codes and restrooms?

The impact of a victory for Bostock and Zarda would be greatest in 28 states that have little or no workplace protection for gay men and lesbians. But even in states such as New York, which does, incorporating sexual orientation in the federal law barring discrimination based on race, color, religion, sex, or national origin would add an important layer of protection.

Federal appeals courts have been split on the question since 2017, when the U.S. Court of Appeals for the Seventh Circuit became the first to rule that gay men and lesbians should be covered. The Second Circuit ruled for Zarda last year, but the Eleventh Circuit, based in Atlanta, ruled against Bostock.

Congress has debated the issue for decades but has "repeatedly declined to pass bills adding sexual orientation to the list of protected traits" under the law, the Justice Department notes. That argument likely will carry weight with some justices, who would prefer a legislative solution.

The Trump administration and the employers being sued claim that turning a blind eye to a person's sex could threaten dress codes, physical fitness requirements and even separate restrooms for men and women, all of which have been upheld by courts until now.

The fired employees, on the other hand, argue that a same-sex relationship should be as sacrosanct as an interracial marriage. Discriminating against them, they say, is akin to applying sex-based stereotypes that have been struck down in courts for decades.

More than 200 companies representing more than 7 million workers have lined up with the employees, contending that "the U.S. economy benefits from a diverse workforce."

Many religious organizations, however, are rooting for the employers. The U.S. Conference of Catholic Bishops says opening employment protection to gay men and lesbians could adversely affect faith-based schools, health care providers and homeless shelters that seek to abide by their own "religious and moral convictions."