Tacoma families with daughters in school sports could face a new requirement if Initiative 638 passes: medical documentation verifying every girl's biological sex before she can compete.

Gov. Bob Ferguson on Tuesday, Sept. 29, formally urged voters to reject the measure, which would bar transgender girls from competing on girls' teams at K-12 public schools statewide. The Tacoma City Council is among the named opponents. The No Hate in Washington State campaign, which organized the opposition alongside Ferguson, cited Councilmember Olgy Diaz as explaining the council's position and called Tacoma the first city in the state to formally oppose I-638.

"Washingtonians should know that I-638 won't create opportunities for girls but it will force them into invasive sex verification exams in order to participate in sports," Ferguson said in a statement, as first reported by The Seattle Times.

The initiative, formally titled the "Defending Equity in Interscholastic Sports Act," would require all students competing in girls' sports to submit medical documentation. Under the initiative's text, verification could involve examination of a student's reproductive anatomy, genetic makeup or testosterone levels.

Let's Go Washington, the conservative political committee backing I-638, disputes that characterization. Spokesperson Hallie Herzberg said the initiative would only require a student's doctor to confirm sex using existing medical records or the doctor's own knowledge of the patient.

The dispute extends to the state voter guide. Let's Go Washington described the requirement as a standard procedure during visits for care "recommended by the American Academy of Pediatrics."

The AAP asked the group to remove its name, saying neither its local chapter nor national organization has weighed in on I-638. Let's Go Washington declined.

The measure carries particular weight in Tacoma. The U.S. Department of Education's Office for Civil Rights placed Tacoma Public Schools under a federal Title IX investigation on Jan. 14, following complaints that the district allows students to play sports based on gender identity rather than biological sex. TPS was one of 18 educational entities nationally under such an investigation, according to The News Tribune. The district said at the time that it would not comply, saying the order conflicted with state law.

The Washington Interscholastic Activities Association (WIAA) has allowed transgender athletes to compete on teams consistent with their gender identity since 2007. According to Seattle Times reporting, the WIAA has said only five to 10 transgender students play sports statewide, out of 1.2 million students.

The U.S. Supreme Court ruled on June 30 that states can ban transgender girls from girls' school athletics without violating the 14th Amendment or Title IX. That ruling does not require Washington to change its policy but clears the legal path for I-638 if voters approve it.

A Ballot Initiative Strategy Center poll of 400 Washington voters found 43% planned to vote in favor of the initiative. Pierce County ballots will be mailed on Tuesday, Oct. 13, and are due by 8 p.m. on Tuesday, Nov. 3.