JACKSON, Miss. (AP) — A transgender girl from Mississippi’s Gulf Coast who wanted to wear a dress to a regional band event was discriminated against when her school insisted she follow a dress code based on her sex assigned at birth, according to a new civil rights complaint.

The American Civil Liberties Union and the ACLU of Mississippi want the Harrison County School District to get rid of its sex-based distinctions in the dress code and stop enforcing the rules in a way that discriminates against girls, according to an administrative complaint filed Wednesday with the U.S. Department of Education’s Office for Civil Rights.

The ACLU says the district’s dress code violates Title IX, the 1972 law originally passed to address women’s rights. The law prohibits discrimination on the basis of sex by any educational programs or activities that receive federal money. The district rule that students’ clothing must match their sex assigned at birth was added to the dress code policy relatively recently, in July 2023.

The district did not immediately respond to a phone message and email seeking comment Thursday.

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The complaint was filed Wednesday on behalf of a woman and her daughter, a 16-year-old student at Harrison Central High School. According to the complaint, the school’s principal told the transgender girl she “can’t represent our school dressed like that” by wearing a dress to the band event, and threatened the student with in-school suspension.

Despite pleas to participate, she was told to ask her mother to bring “boys’ clothes” or face exclusion from the event, the complaint said.

The transgender teen’s story “is emblematic of other girls at Harrison County School District who have complained of the discriminatory dress code and hostile learning environment for LGBTQ+ students,” said McKenna Raney-Gray, an LGBTQ Justice Project attorney at the ACLU of Mississippi.

The complaint also wants the Office for Civil Rights to investigate the district focusing on Title IX discrimination.

The girl’s mother said she is deeply concerned about the district’s practices.

“Transgender and gender nonconforming students should not be forced to choose between participating in school events or remaining true to their gender identity,” the mother said.