The Democratically controlled House of Representatives voted Friday 236-173 in favor of the Equality Act, which would require schools to include male athletes who identify as transgender girls on female sports teams.
Eight Republicans crossed party lines to vote for the bill, which had unanimous Democratic support.
The bill amends the Civil Rights Act of 1964 to make "sexual orientation and gender identity" protected characteristics under federal anti-discrimination law.
Among other things, that would force public schools to expand female athletic teams to include biological males who identify as transgender girls.
Republican Florida Rep. Greg Steube introduced a last-minute amendment to the bill that would have preserved Title IX's protections of female athletic teams, but Democrats rejected it.
Every House Democrat but one co-sponsored the legislation. The only Democrat who wasn't a co-sponsor, Illinois Rep. Dan Lipinski, announced his support for the bill following pressure from left-wing activists.