The U.S. Education Department said it is investigating Denver Public Schools for alleged discrimination after the district converted a girl’s restroom on the second floor of East High School into an all-gender restroom while leaving the other bathroom exclusively for male students.

Denver Public Schools called the decision to investigate the conversion of a women’s restroom into an all-gender facility as potential discrimination “unprecedented.”

An all-gender restroom at East High School in Denver is the subject of an investigation launched by the U.S. Department of Education.