The U.S. Department of Education on Thursday said Denver Public Schools broke Title IX, the federal law banning discrimination on the basis of sex in education, when it created all-gender bathrooms.

The agency said the district didn’t let students use facilities consistent with their “biological sex.”

The Department of Education’s Office for Civil Rights began an investigation of East High School in January after the district converted a female restroom into a facility that could be used by all genders.

District leaders said the all-gender restroom included 12-foot-tall partitions around toilets. The district also created a second all-gender bathroom on the floor to address fairness concerns.

District officials have said the all-gender bathrooms were created in response to a student-led process and still leave students access to traditional male and female restrooms as well as single-stall, all-gender bathrooms throughout the school.

The Education Department sent Denver Public Schools a draft resolution that laid out four conditions that must be met within 10 days in order to avoid enforcement action.

The resolution would require the district to:

Designate all all-gender, multi-stall restrooms as sex-segregated facilities.

Repeal any policy that allows students to use the bathrooms and changing facilities on the basis of gender identity, instead of biological sex.

Define “male” and “female” for purposes of Title IX with “biology-based definitions” and reflect these definitions in “all other policies and practices.”

Send a written memo to schools reiterating that the “school’s intimate facilities must be safe, clean, and consistently available, while also protecting student privacy, dignity, and safety, and must be comparably accessible to students of both sexes.”

The department says if the district does not agree to the resolution plan, it could take enforcement action. Such actions can include financial penalties or the removal of federal funding.

Acting Assistant Secretary for Civil Rights Craig Trainor said the move “undermined” students’ privacy and safety.

“Denver Public Schools 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 a statement.

“Denver is free to endorse a self-defeating gender ideology, but it is not free to accept federal taxpayer funds and harm its students in violation of Title IX,” he continued. “The Trump Administration will work relentlessly to hold accountable school districts that harbor the ideological fanatics and policies that sully students’ educational experience with sex discrimination.”

The district has defended its decision saying that the process came from students and that the all-gender bathrooms are in response to students’ needs. District officials have also pointed to the district’s attention to privacy and security concerns.

Denver Public Schools has not publicly addressed the department’s findings but has previously said students have several bathroom options including all-gender, single-stall bathrooms that provide additional privacy.

The issue is one that’s being debated across the country. Earlier this year, President Donald Trump issued an executive order banning transgender girls from playing on sports teams that don’t align with their biological sex.

And Republicans in Congress have also attempted to pass legislation that would prevent transgender students from using school bathrooms and sports teams that align with their gender identity.

The Education Department has also targeted other schools over their gender policies, including a case at a university where officials said the school was engaging in unlawful diversity, equity, and inclusion (DEI) practices in violation of Title VI just this week.

Denver Public Schools now faces a decision about whether to comply with the resolution plan or risk potentially millions of dollars in federal funding.

The district now has 10 days to decide whether to accept the resolution plan and roll back its all-gender bathroom policy.