The Education Department determined on Thursday that Denver Public Schools’ bathroom policy is in violation of federal civil rights law.

DPS’s policy allowing students to use private facilities corresponding to their “gender identity” rather than their biological sex is out of compliance with federal regulations, the department said, as well as the school district’s move to convert sex-separated multi-stall restrooms into “all-gender” facilities. The agency’s Office for Civil Rights said the policies violate Title IX, which extends protections against discrimination on the basis of sex, by allowing males to “invade sensitive female-only spaces,” and vice versa.