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(AP) A western Pennsylvania school district wants a federal judge to dismiss a lawsuit by three transgender students challenging a rule requiring students to use either unisex restrooms or those corresponding to their biological sex.

The Pine-Richland High School students, two born biologically male who now identify as female and one born biologically female who identifies as male, sued in October. They say the district let students use restrooms based on their gender identities for years until the school board passed a resolution changing the practice in September while it researches adopting a formal policy.

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In a Friday filing, the district asked that a federal judge not issue a preliminary injunction that would force the district to let transgender students use restrooms that conform to their gender identity until the lawsuit is resolved.

The district said the Justice Department contradicted the law in May when it sent a guidance letter saying schools could lose federal funding if they don't expand the Title IX protections to include "gender identity."

The Title IX federal discrimination law defines sex biologically - not by a person's stated gender identity - so the lawsuit and the request for a preliminary injunction should be dismissed, the district argued.

Under Title IX, the term "sex" refers to "a fixed, binary and genetically-determined sex, based on the nature of human reproduction and the irrefutable fact that we are a species of males and females," the district argued.

In response, Lambda Legal, the advocacy group representing the transgender students, issued a statement calling the district's argument "shameful."

"The hard-line stance taken today by the Pine-Richland School District show how far the school district has strayed from its mission to educate and serve all its students," Lambda staff attorney Omar Gonzalez-Pagan said.

"A person's sex is determined by multiple factors, including hormones, external and internal morphological features, external and internal reproductive organs, chromosomes and gender identity. ... Gender identity - a person's internal sense of their own gender - is the primary factor in determining a person's sex," Lambda contends.

A court hearing in the case has not yet been set.

The U.S. Supreme Court and the 3rd U.S. Circuit Court of Appeals, whose jurisdiction includes Pennsylvania, haven't ruled on whether Title IX includes gender identity protections, so the Pine-Richland case could set precedent for the circuit.

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The school board resolution came months after a female student's father complained that her privacy was being violated when she encountered "transgender girls i.e. individuals with male genitalia who believe themselves to be girls" in the girls' restroom, the district said in its Friday filings in U.S. District Court. That student has since left the district and enrolled in a private school "to ensure that her constitutionally protected right to privacy would be protected," the district said.

The district further maintained that even if the Title IX definition were expanded, the district's restroom policy would be legal to protect the privacy rights of non-transgender students.