Does a US employer have the right to sack a worker because they are gay or transgender?
That question, which has caused deep divisions within US society, will go before the Supreme Court at a time when the political scene has already reached fever pitch over efforts to impeach President Donald Trump.
The Trump administration has effectively thrown in its lot with the employers, backing a narrow interpretation of a 1964 civil rights law banning discrimination "on the basis of sex".
"Sex refers to whether you were born woman or man, not your sexual orientation or gender identity," argued Solicitor General Noel Francisco, representing the government's position before the court. He said it is the job of Congress to update the law, not the justice system.
But advocates for sexual minority groups argue that the rights of the LGBTQ+ community have advanced first and foremost through the court system in recent years, most notably with the Supreme Court's landmark 2015 decision to legalise same-sex marriage.
The US Supreme Court will consider whether anti-discrimination laws cover gay, lesbian, bisexual and transgender employees. Source: Getty Images
"In many ways, this is more fundamental than what was at stake" in the same-sex marriage case, Ria Tabacco Mar of the American Civil Liberties Union (ACLU) said.
"We're talking about the ability to earn a living, the ability to support our families, the ability to secure a safe place to live. I mean, this goes to the very heart of what it is to live and work in this country."
Only 22 states forbid . Ms Tabacco Mar said it was up to the Supreme Court to stop the LGBTQ+ community from being "relegated to second class status."
'Enough is enough'
The Supreme Court will start by hearing the cases of Donald Zarda and Gerald Lynn Bostock.
The former, a skydiving instructor from New York, was sacked after jokingly reassuring a female client whom he was strapping to himself for a jump that he was gay. He died in a base-jumping accident in 2014, but his family have pursued the case.
The second case is of a social worker from Georgia who was sacked shortly after joining a gay sports team.
Mr Zarda's dismissal was overturned by a court while Mr Bostock's was upheld, and the difference in interpretation of the law prompted the intervention by the Supreme Court.
The court's nine justices will then examine the case, for the first time in public, of a transgender person.
Aimee Stephens, 58, worked for a Detroit funeral home for six years before telling her employer she wanted to be issued a female uniform. Two weeks later, she was fired, with the boss saying: "This is not going to work."
The boss, Thomas Rost, cited his Christian values in defending his decision and the need to avoid upsetting customers in mourning.
Distraught, Ms Stephens decided to fight. "It was time that somebody stood up and said enough is enough," she said. "Every human being deserves the same rights. That's all we are asking for."
'Too early'
Since its landmark decision on gay marriage, the court has swung to the right with Mr Trump's appointment of two conservative judges, Neil Gorsuch and Brett Kavanaugh.
For lawyer Tom Goldstein, who has often argued cases at the Supreme Court, Ms Stephens' case has probably come "too early" before the body, which is unlikely to accept a broader reading of the 1964 law.
"In 20 years, I think it's going to be pretty inconceivable socially, that we will think that the discrimination against gays and lesbians and transgender individuals is legal," he said.
"But we are in a kind of transitional period. And I think that the conservatives, as a result, are more likely to take a more traditional view of the statute."
Employers have also received support from conservatives and religious groups.
Catholic bishops wrote an amicus brief to the court warning that "ordinary religious believers, whose views about marriage and human sexuality do not conform to those of the present culture, will be silenced or punished for 'unwelcome' speech on these subjects, which now will be regarded as a form of harassment."
The conservative group "Alliance Defending Freedom," which successfully backed a baker who refused to make a wedding cake for a gay couple and whose case ended up before the Supreme Court, has also weighed in on the side of employers.
Workers who feel their rights have been infringed upon can count on the support of many advocacy groups, including the ACLU, and the backing of Democratic politicians.
The two sides will find themselves face to face Tuesday when rival demonstrations are set to be held outside the court as the hearings get under way.
