Gay workers and their corporate supporters won a legal victory over the Trump administration as a federal appeals court ruled that firing people over their sexual orientation is a form of illegal sex discrimination.

The appeals court in Manhattan overturned its own previous rulings, saying "legal doctrine evolves." It's the second ruling in the U.S. to break with precedent in finding that workplace discrimination based on sexual orientation is illegal. A third appeals court ruled the other way last year. The split among the courts sets up a possible Supreme Court showdown.

"Sexual orientation discrimination — which is motivated by an employer's opposition to romantic association between particular sexes — is discrimination based on the employee's own sex," Judge Robert Katzmann wrote in an opinion for the full court's majority on Monday.