The U.S. Department of Education said on Tuesday its civil rights office is investigating the Portland, Oregon, school system for allowing a transgender high school runner to compete in female sports and use girls’ locker rooms.

The department’s Office for Civil Rights also said it is investigating the Oregon School Activities Association, which oversees high school sports in the state, and its policy of generally allowing transgender students to play gender-specific sports that do not correspond to their sex at birth.

Gender in schools has been a key issue for President Donald Trump and a hot-button topic around the country.

In a January executive order, Trump said the previous administration had “harmed women” by trying to extend protections under Title IX of the federal Civil Rights Act to transgender Americans, and Trump’s administration has spoken out against what it calls the “dangerous and unfair participation of men in women’s sports.”

“We will not allow the Portland Public Schools District or any other educational entity that receives federal funds to trample on the anti-discrimination protections that women and girls are guaranteed under law,” said Craig Trainor, the Department of Education’s acting assistant secretary for civil rights.

Kimberlee Armstrong, the superintendent of Portland Public Schools, said in a written statement that the system was cooperating with the federal investigation. She said that her schools are “in full compliance with Oregon state law, which may differ from federal guidance.”

“I stand firm in our legal responsibilities, and I deeply value every student’s right to be treated with dignity, safety, and respect,” Armstrong said.

The Oregon School Activities Association said in a written statement that it had received an investigation notice from the Department of Education, and that it was consulting with its legal counsel on how to respond.

The Department of Education said in a statement that its investigation under Title IX of the Civil Rights Act is related to the school district and state officials allowing a transgender girl to compete in the 200 meter and 400 meter events at the Portland Interscholastic League Championship both last year and this year. The statement said the athlete easily won the events both years.

If found to have violated Title IX, a school can face penalties including loss of federal funding. Settlements have historically been more common.