The initiative, approved by voters last week by an 11-point margin, is scheduled to take effect Dec. 3 unless a judge strikes it down or pauses its implementation. Under the measure, any student who wants to play on a team designated for girls must verify their sex assigned at birth as part of a routine sports physical, using reproductive anatomy, genetic makeup, or normal endogenously produced testosterone levels.

The plaintiffs include TransFamilies, a Washington-based nonprofit; the Washington Education Association; and parents of students who play girls' sports in public schools. In their complaint, they argue the law is unconstitutional on multiple grounds.

Specifically, the plaintiffs contend that requiring sex verification "significantly intrudes on students' privacy rights guaranteed by Article 1, Section 7" of the state constitution. They also argue the measure violates the state's Equal Rights Amendment by imposing the verification requirement on all girls while not applying the same requirement to boys.

The lawsuit follows a vote that drew national attention and intense local debate. On election night, supporters and opponents offered sharply different views of what the measure means.

"Every girl in Washington state deserves a safe place to play sports," said Diane Bedwell, co-chair of No Hate in WA State.

Brian Heywood, founder of Let's Go Washington, which backed the initiative, said: "I think there can be empathy and sympathy for boys that think they're girls. There can be a solution in the trans sports arena, but it shouldn't come at the cost of every girl that wants to compete, and I think it's that simple."

The Washington Interscholastic Activities Association, which governs high school sports in the state, said it is preparing to implement the law while the legal challenge proceeds. In a written statement, a WIAA spokesperson said the association "continues to follow current Washington state law" and that its Executive Board has the authority to adjust the WIAA Handbook to align with new state law when the measure takes effect.

The WIAA said it will have all necessary changes in place by Dec. 3, but that implementation details, including updates to requirements for physicals, are undergoing legal review. Updated forms and guidance will be provided to schools once that review is complete.

The lawsuit is the latest development in a broader legal and political fight over transgender student athletes in Washington. The Seattle school board previously authorized legal action over the initiative, and the measure was widely expected to face court challenges regardless of the vote outcome.

With the Dec. 3 effective date approaching, the case now rests with the King County courts, where a judge could decide whether to block the law while litigation continues. For students, parents, and school officials across the state, the outcome will determine whether the new verification requirements take effect as scheduled or are delayed or struck down.