In a letter on Thursday, the U.S. Department of Education said Denver Public Schools broke federal law by opening all-gender bathrooms and allowing students to use whichever bathroom they identify with rather than their assigned biological sex.

In January, the department’s Office for Civil Rights began investigating the district’s decision to convert a girls’ bathroom into an all-gender restroom at East High School. School officials said they thought their decision was in line with federal guidance on Title IX, the civil rights law barring sex discrimination in education. But the government said that wasn’t the case.

In a letter to Denver Public Schools, the federal government provided a proposed resolution for the district’s consideration. The four-point plan would require the district to take a number of actions within 10 days to “come back into compliance with Title IX and its implementing regulations” and avoid potential enforcement action by the department.

Denver Public Schools received the letter from the federal government Thursday. “We are reviewing the resolution before we determine our next steps,” district officials said.

Allowing Students to Use Bathroom of Their Choice

In the letter, Acting Assistant Secretary for Civil Rights Craig Trainor said the school district violated Title IX by converting a restroom designated for girls into an all-gender facility and by allowing students to use the school’s bathrooms based on their gender identity rather than their biological sex.

“Denver Public Schools (DPS) has violated Title IX and its implementing regulations by converting a sex-segregated restroom designated for girls in East High School to an ‘all gender’ facility and by allowing students to use the high school’s intimate facilities on the basis of their gender identity rather than their biological sex,” Trainor said in the letter. “DPS’s policy endangers student safety, privacy, and dignity.”

Trainor said the decision to convert the bathroom “unequally distributed” school bathrooms between students of different sexes and “created a hostile environment for students by encouraging the presence of unrelated males in a former girls’ restroom.”

An all-gender restroom was later introduced on the same floor as the original all-gender restroom to “mitigate concerns of fairness,” according to Trainor.

District officials have said that students still have access to all-boys and all-girls bathrooms, and that students who wanted more privacy could use a single-stall, all-gender restroom, according to reporting by The Colorado Sun.

Trainor also cited the privacy and security of the bathrooms as an area of concern, writing in his letter, “the creation of an all-gender multi-stall restroom without lockable doors and stall partitions that obscure the body and reach all the way up to a student’s shoulder blades also raised concerns about student safety and privacy.”

Trainor wrote that although Denver Public Schools has opened up a second all-gender restroom, the department was “alarmed that DPS’s updated restroom did not feature significant enhancements that would give students confidence in their privacy and security.”

Trainor also said Denver Public Schools would need to “rescind its biology-denying policies and practices” and re-establish sex-based definitions of “male” and “female” in all Title IX policies and practices in the school district.

“We demand that you commit to rescinding your biology-denying policies and practices and to re-establishing biology-based definitions of ‘male’ and ‘female’ in all of your Title IX policies and practices, including your policies and practices related to the use of intimate facilities,” Trainor wrote.

The resolution also demands the district send a memorandum to all schools that states that “bathrooms must be allocated and used in a manner that protects the privacy, dignity, and safety of all students while ensuring that they are equally accessible to students of both sexes.”

Federal Government Threatens to Cut Millions in Federal Funding

The federal government proposed a four-point resolution that Denver Public Schools would have to accept in full and act on within 10 days to avoid enforcement action from the Education Department. In a statement on the resolution, Trainor said the department was “working relentlessly to hold accountable school districts that harbor the ideological fanatics and policies that sully students’ educational experience with sex discrimination.”

In a statement, U.S. Education Secretary Betsy DeVos said the department “will not stand by while a school district forces children into uncomfortable and unsafe situations that also may put the privacy and dignity of all students at risk. We have resolved many such cases in the past with districts working to right the ship in good faith,” DeVos added.

The statement by Trainor also called for the district to “send a memo to all schools stating that any restroom is to be equally accessible to students of both sexes, and the bathrooms must be used in a manner that protects the privacy, dignity, and safety of all students.”

In the letter to the district, the government added a fourth action point that said, “if DPS does not accept this resolution within 10 days of receipt of this letter, we may recommend enforcement measures.”

The letter ends by saying, “we ask that you respond by April 15 to confirm that you have accepted this resolution.”

Failure to accept the proposed resolution could see the federal government cut off millions of dollars in federal funding to Denver Public Schools, the district’s spokesman, Tom Burnham, previously said.

State Republican Groups Celebrate Move

In a statement, Republican State Leadership Committee spokeswoman Brooke Crowley said it was “vindication” for their legal efforts.

In the past, the RSLC has raised money to pay for court cases contesting gender identity policies that allow transgender girls to compete on girls’ sports teams. “This vindication, in part, resulted from the RSLC’s financial and legal support of an ongoing federal lawsuit by three young women from the state of Colorado,” Crowley said.

Laura Schauer Iarocci, director of federal advocacy for the American Principles Project, said, “This is one more case of Title IX being enforced on behalf of female students.” Schauer Iarocci is also a lawyer who has filed a lawsuit against the Denver school board over the bathroom policy.

“Biological sex has a definition and schools must use the biological definition of male and female and only refer to that if they are going to use Title IX,” Schauer Iarocci said in the statement.

Schauer Iarocci is part of a lawsuit by the Denver group Tertio contra Aries that is “seeking to reinstate specific references to ‘biological sex’ as male and female as essential to defining ‘sex,’” according to court documents reviewed by Colorado Peak Politics.

Rep. Liz Cheney (R-WY) celebrated the Department of Education’s decision.

“The Trump Administration’s Education Department is standing up for the privacy and safety of women and girls,” Cheney said in a statement. “The decision made by DPS leadership to open the bathrooms to all students, regardless of biological sex, is a direct threat to the privacy and safety of women and girls. All students have the right to attend school free from harassment, abuse, or assault, and I am glad to see this administration working on their behalf.”

Department Continues Crackdown on Transgender Girls in Sports

President Donald Trump signed an executive order earlier this year that made it easier for schools to ban transgender girls from participating on sports teams that align with their gender identity but not their biological sex.

Federal civil rights investigations, lawsuits, and legislation against transgender girls have continued since Trump signed the order. The day of the executive order, the federal government also said transgender girls may not play on women’s sports teams unless their schools comply with Title IX guidelines. The guidance came from the Departments of Justice and Education.

GOP lawmakers in Congress have also proposed legislation to bar transgender students from using bathrooms that match their gender identity and from participating on sports teams that do not match their biological sex.

The Education Department also said this week that George Mason University violated federal law on unlawful diversity, equity, and inclusion (DEI) practices under Title VI.