A West Virginia law that prohibits transgender girls from playing on girls sports teams violates Title IX and the equal protection clause of the U.S. Constitution, the U.S. Department of Justice said Thursday.

The Justice Department sided with an 11-year-old girl who has sued over her state’s new law, one of a wave of at least seven similar measures passed by states around the country this year.

The arguments, outlined in a “statement of interest filing,” are one of the most direct challenges the Biden administration has made to state-level restrictions for transgender students to date.

“To be sure, there remain significant barriers to providing full equity in athletics for female students,” the Justice Department said in its filing. “But permitting participation by transgender girls, who make up ‘approximately one half of one percent’ of the United States’ population, is not one of them.”

The brief, which argues that the West Virginia law is based on “misinformation and fear,” is in line with the administration’s stated position on the issue. It comes a day after the U.S. Department of Education released a memo clarifying its position that the sex-discrimination protections in Title IX prohibit discrimination on the basis of sexual orientation and gender identity.

The plaintiff in the case, Becky Pepper-Jackson, was assigned male at birth but identified as a girl by 3rd grade. Becky, who is 11 and started taking puberty-delaying treatments last year, has been on a school cheerleading team in Harrison County, W. Va., and she hopes to compete on the girl’s cross-country team in middle school, her suit says.

But she won’t be allowed to under the state’s new law, H.B. 3293. Because she can’t play on a team that aligns with her gender, she will be effectively shut out of participating in team sports throughout her K-12 experience, the Justice Department argued.

“B.P.J. does not seek to join the boys’ cross-country and track teams because she is a girl and such participation would ‘devastate’ B.P.J., ‘completely erase who she is,’ and undermine her social transition,” the legal filing argues.

The agency’s legal arguments rest in part on the U.S. Supreme Court’s 2020 decision in Bostock v. Clayton County, Ga., which held that a prohibition of sex discrimination in Title VII, the federal employment law, prohibits unequal treatment on the basis of sexual orientation or gender identity. The Biden administration, and several preliminary court filings in other cases, have held that that precedent should inform interpretations of Title IX, which prohibits sex discrimination in education.

“The Supreme Court has recently clarified that discrimination against a person for being transgender is discrimination based on sex,” the filing says, citing Bostock.

In addition, the West Virginia law will affect girls unfairly, because it says “athletic teams or sports designated for females, women, or girls shall not be open to students of the male sex.” The law defines male sex as “sex assigned at birth,” effectively banning transgender girls from girls’ sports, but it has no corresponding restrictions for transgender boys.

The law’s restrictions may also affect cisgender girls, the Justice Department argued, because girls who don’t present as “stereotypically feminine” may be subject to challenges of the eligibility or gender.

The federal brief also questioned the motivations of the West Virginia bill’s sponsors, flagging instances of “outright anti-transgender bias.”

For example, Delegate Margitta Mazzoch, who co-sponsored the measure, said that she did not “want all this mixing and matching” of transgender and cisgender children in “locker rooms,” the filing says.

Supporters of similar state bills around the country have said they are necessary to ensure fairness in girls’ sports. And some have questioned the legitimacy of transgender identity.

An attorney Alliance Defending Freedom, a conservative legal group that has argued against transgender-inclusive policies, has slammed the Biden administration’s position as “forcing radical gender identity ideology on everyday Americans by effectively rewriting Title IX.”

The administration has not yet released guidance on how schools should accommodate LGBTQ students or directly challenged one of the new state laws in court.

In addition to the West Virginia filing, the Justice Department also filed a statement of interest Thursday in a legal challenge over an Arkansas law that prohibits gender-affirming care for transgender youth.