(CNN) A new genre of employment discrimination cases that could be the next battleground for supporters of LGBT rights are hurtling towards the Supreme Court.
More than two years after the Supreme Court cleared the way for same-sex marriage nationwide, plaintiffs want the justices to enable employees to use existing civil rights law to sue for discrimination based on sexual orientation.
On Tuesday, a federal appeals court based in New York will hear arguments in one such case, and later this fall the Supreme Court will consider whether to take up a separate challenge.
At the heart of the cases are whether Title VII of the Civil Rights Act of 1964, a federal law that bans employment discrimination because of sex, also protects claims of sexual orientation. In an unusual twist in the case, the Trump administration is on opposite sides from the Equal Employment Opportunity Commission -- a federal agency charged with enforcing Title VII.
Joshua Matz, a lawyer who has has written about the issue for the Take Care law blog, said the Supreme Court will likely take up the issue. "It's a matter of national importance, affecting employees and employers from every walk of life," he said.
Most courts have rebuffed such challenges over the years, but last April, the 7th US Circuit Court of Appeals broke new ground when Judge Diane Wood, a Clinton appointee writing for the majority, allowed a claim from Kimberly Hively to go forward. Hively sought to sue Ivy Tech Community College arguing that the school violated Title VII when it denied her employment based on her sexual orientation.
"Any discomfort, disapproval, or job decision based on the fact that the complainant -- woman or man -- dresses differently, speaks differently, or dates or marries a same-sex partner, is a reaction purely and simply based on sex," Wood wrote. "That means that it falls within Title VII's prohibition against sex discrimination, if it affects employment in one of the specified ways."
In short, Wood held that claims of sexual discrimination encompass claims of discrimination based on sexual orientation because similarly situated people are treated differently solely on account of their sex.
"For instance," said Matz,"if an employer fires a female employee because she is married to a woman, but would not fire an otherwise identical male employee married to a woman, the employee's sex is properly seen as having caused the termination."
Supporters of LGBT rights call the 7th Circuit opinion a landmark decision, but critics say that that the law was not written to provide a remedy for claims of sexual orientation.
"The two traits are categorically distinct," wrote Judge Diane Sykes in a dissent.
Hively's employers have decided not to appeal the case, so it will remain on the books. But two other cases are moving forward.
Lawyers for Jameka Evans, a security guard who claims her employer, a hospital, violated Title VII by discriminating against her because of her sexual orientation lost her fight in the 11th US Circuit Court of Appeals and her lawyers are asking the Supreme Court to take up her appeal.
Separately, on Tuesday, the 2nd US Circuit Court of Appeals will hear a claim brought by the estate of Donald Zarda. Zarda, a skydiving instructor, died before trial, but his estate has continued his suit.
The case stems back from 2010 when Zarda was an Altitude Express instructor for Rosanna Orellana. Zarda's role was to be tied to the back of Orellana, deploy the parachute and supervise the jump. According to court papers, at some point Zarda informed Orellana that he was gay. After the jump, Orellana's boyfriend learned that Zarda had disclosed his sexual orientation and called Altitude Express with various complaints about Zarda's behavior. Zarda was fired.
The company contended that Zarda was fired for failing to provide an enjoyable experience to customers. Zarda asserted that his actions were appropriate and he was fired because of his sexuality -- he filed a complaint with the EEOC alleging sex discrimination in violation of Title VII.
The case is in an unusual position as the EEOC supports Zarda, while the Justice Department is on the other side.
"The EEOC is not speaking for the United States," DOJ lawyers say in their brief. They stress that Congress did not mean Title VII to extend to claims of sexual orientations.
Coming more than two years after the Supreme Court cleared the way for same sex marriage, government lawyers note "to be sure" there have been "notable changes in societal and cultural attitudes about such discrimination" but they insist that Congress has "consistently" declined to amend Title VII in light of those changes.
They say that even changes in societal attitudes "do not present courts with a license to rewrite a constitutionally valid statutory text under the banner of speculation about what Congress might have done to implement a clear statute's policy objectives. "
Lawyer Gregory Antollino and the LGBT rights group Lambda Legal will argue in support of Zarda's estate.
"If you discriminate on the basis of sexual orientation, you necessarily take into account the sex of the employee," said Antollino. "You can't take the 'sex' out of "sexual orientation."