Washington voters approved Initiative 638 on Wednesday, banning transgender girls from competing in K-12 girls' sports.

The ballot measure passed with about 56.6 percent support and 43.4 percent opposition as vote counting continued, according to the Washington secretary of state's office. The Associated Press called the race for the initiative on Wednesday evening.

Initiative 638 reverses a 2007 policy from the Washington Interscholastic Activities Association that had permitted transgender students to participate on teams matching their gender identity. Under the new rules, students seeking to join girls' teams must submit verification from a health care provider confirming their biological sex based on reproductive anatomy, genetic makeup, or endogenous testosterone levels.

The measure applies only to female sports categories, and boys' teams face no similar requirements. It covers public and private K-12 schools competing through the WIAA and takes effect December 3, 2026.

Supporters, including the conservative group Let’s Go Washington, argued the change ensures fairness for female athletes. The initiative joins similar measures advancing or passing in states such as Colorado, Arizona, and Nebraska this cycle.

Opponents described the verification process as potentially invasive and criticized it as unnecessary given the small number of affected athletes. The result marks a notable shift in a state long considered a leader in policies aligned with gender identity.

More than two dozen states have enacted comparable restrictions on transgender participation in youth sports, primarily through legislative action. Washington's outcome demonstrates voter support for biological sex-based categories even in a Democratic stronghold.