Transgender-rights supporters marched through downtown Seattle Thursday after Washington voters approved a measure barring biological males from girls’ K–12 interscholastic sports, setting up a potential court battle over the new restrictions.

Demonstrators gathered at Westlake Park before marching toward Pike Place Market, according to KUOW. The protest followed the passage of Initiative 638, which also requires students seeking to compete in girls’ sports to provide medical verification of their biological sex.

The measure had 56.8% support in returns reported Thursday by FOX 13 Seattle. The Associated Press called its passage Wednesday evening, with ballots still being counted.

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"I was kind of expecting it, but it was still devastating nonetheless," Evan Gortner of Gender Equity Movement, which organized the protest, told KUOW.

Marchers chanted, "638 is trans hate." Some attendees also criticized Democratic leaders for not doing more to defeat the initiative.

The result delivered a victory to Let’s Go Washington, the conservative group behind the measure, even as voters rejected two other initiatives it backed concerning parental rights and the repeal of the state’s tax on high earners.

Supporters argue that separating girls’ sports by biological sex protects fairness, safety and athletic opportunities for female students. Opponents contend the restrictions discriminate against transgender students and could subject girls to intrusive medical verification.

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The dispute now extends beyond the election results.

Gender Justice League Executive Director Danni Askini told KUOW her organization was consulting partners and evaluating a possible challenge on student-privacy grounds. The group had not formally announced a lawsuit in that Nov. 5 report.

The ACLU of Washington also condemned the outcome, but told KUOW it does not discuss potential litigation. That response did not announce a lawsuit.

Washington Democrats, meanwhile, have said they support other organizations pursuing challenges but will not bring a case themselves.

"WA Dems will not be challenging the initiative in court. We believe there will be organizations who do and we support those efforts," the party previously told OutKick.

Party Chair Shasti Conrad called the initiative unconstitutional in a Nov. 5 statement.

The measure’s medical-verification requirement has become a central point of contention.

Its text requires a health examination and consent form, or another statement signed by a student’s personal healthcare provider, verifying biological sex as part of the required routine sports physical. That verification must rely on reproductive anatomy, genetic makeup or naturally produced testosterone levels. The text does not prescribe a particular examination or test.

Washington has allowed students to compete on teams consistent with their gender identity since 2007.

The debate also prompted protests from female athletes before the election. About a dozen Camas girls declined to race against a transgender teammate on Oct. 13, OutKick previously reported.

For schools, the immediate question is how to carry out the new requirements.

The Washington Interscholastic Activities Association told KUOW it was preparing changes for Dec. 3 and reviewing implementation, including physical-examination requirements. It said updated guidance and forms would go to schools after legal review.