Florida has become the latest US state this year to ban transgender girls and women from participating in female sports at public schools.
The state’s Republican governor Ron DeSantis signed the measure into law on Tuesday.
The law says women and girls must play on the terms of the “biological sex” on their birth certificate.
LGBT activists have denounced the move as “discriminatory”, with one group vowing to launch a legal challenge.
DeSantis signed the measure on the first day of Pride Month, an annual celebration of the LGBT community in June.
“We believe that is very important that the integrity of these competitions are preserved,” the governor said as he signed the law at a Christian school in Jacksonville city.
“We’re gonna go based on biology, not based on ideology when we’re doing sports.”
The move comes as Republican-led states push back against pro-LGBT policies supported by the administration of Democratic US president Joe Biden.
Florida’s law defines an athlete’s sex as that stated on official documents at birth.
Called the Fairness in Women’s Sports Act, the law says sports teams for girls and women “may not be open to students of the male sex”.
It’s not clear whether all female athletes must now show birth certificates to be in sports teams.
The law will apply to public secondary and high schools, colleges and universities when it comes into effect on 1 July.
