This article was co-published by ProPublica, NBC News and the Texas Tribune. ProPublica is a Pulitzer Prize-winning investigative newsroom. Sign up for The Big Story newsletter to receive stories like this one in your inbox.

The U.S. Education Department’s civil rights enforcement arm has launched an investigation into a North Texas school district whose superintendent was secretly recorded ordering librarians to remove LGBTQ-themed library books.

Education and legal experts say the federal probe of the Granbury Independent School District — which stemmed from a complaint by the American Civil Liberties Union of Texas and reporting by NBC News, ProPublica and The Texas Tribune — appears to be the first such investigation explicitly tied to the nationwide movement to ban school library books dealing with sexuality and gender.

The Education Department’s Office for Civil Rights notified Granbury school officials on Dec. 6 that it had opened the investigation following a July complaint by the ACLU, which accused the district of violating a federal law that prohibits discrimination based on sexual orientation and gender. The ACLU complaint was based largely on an investigation published in March by NBC News, ProPublica and the Tribune that revealed that Granbury’s superintendent, Jeremy Glenn, instructed librarians to remove books dealing with sexual orientation and people who are transgender.

“I acknowledge that there are men that think they’re women and there are women that think they’re men,” Glenn told librarians in January, according to a leaked recording of the meeting obtained, verified and published exclusively by the news outlets. “I don’t have any issues with what people want to believe, but there’s no place for it in our libraries.”

Later in the meeting, Glenn clarified that he was specifically focused on removing books geared toward queer students: “It’s the transgender, LGBTQ and the sex — sexuality — in books,” he said, according to the recording.

The comments, combined with the district’s subsequent decision to remove dozens of library books pending a review, fostered a “pervasively hostile” environment for LGBTQ students, the ACLU wrote in its complaint. Chloe Kempf, an ACLU attorney, said the Education Department’s decision to open the investigation into Granbury ISD signals that the agency is concerned about what she described as “a wave” of anti-LGBTQ policies and book removals nationally.

“In this case it was made very clear, because the superintendent kind of said the quiet part out loud,” Kempf said in an interview. “It’s pretty clear that that kind of motivation is animating a lot of these policies nationwide.”

An Education Department spokesperson confirmed the investigation and said it was related to Title IX of the Education Amendments of 1972, which prohibits schools from discriminating on the basis of sex, gender and sexual orientation. The Office for Civil Rights doesn’t comment on pending investigations, the spokesperson said.

If the investigation confirms violations of students’ rights in Granbury schools, the agency can require the district to make policy changes and submit to federal monitoring.

Neither Glenn nor the district responded to messages Monday. In an earlier statement following the news outlets’ reporting in March, the district said it was committed to supporting students of all backgrounds. And the district said that its primary focus is educating students but that “the values of our community will always be reflected in our schools.”

Granbury, a town 40 miles west of Fort Worth, has been embroiled in a heated debate over what types of books children should be allowed to read at school.

Last year, voters in Granbury elected a pair of school board members who campaigned against LGBTQ-affirming school curricula and library books. Afterward, Glenn began asking district administrators about several books that an unnamed school board member had found in the district’s online catalog, according to text messages reviewed by NBC News, ProPublica and The Tribune. The messages from the board member to Glenn included screenshots of eight titles, all of which dealt with LGBTQ topics, with the words “gay,” “trans” and “gender” highlighted in some of the book descriptions.

In January, when Glenn met with librarians, he told them that the new school board was “very, very conservative” and that any employee who holds different political views had “better hide it,” according to the recording of his comments. In the days that followed, the district embarked on one of the largest mass book removals in the state, pulling 130 titles, most of which featured LGBTQ characters or themes.

After a volunteer review committee voted to return all but a few of the titles, two disgruntled members of the committee filed a police report in May accusing district employees of providing “pornography” to children, triggering a monthslong criminal investigation by Hood County Constable Chad Jordan, which remained open as of August. Jordan didn’t respond to messages requesting an update on the investigation.

All of that — including the fact that Glenn has never apologized or walked back his comments — has created an unwelcoming environment for LGBTQ students in the Granbury district, the ACLU argued in its complaint.

“These comments, combined with the book removals, really send a message to LGBTQ students in the districts that: ‘You don’t belong here. Your existence is shameful. It should be censored,’” Kempf said.

In recent months, Granbury parents and voters have continued to pressure the district to remove books with LGBTQ themes or descriptions of sex. Last month, Karen Lowery, one of the women who sought criminal charges against Granbury librarians, won a seat on the school board; she has vowed to purge books that she has deemed inappropriate for children. Of the nearly 80 titles conservative activists want banned, 3 out of 5 feature LGBTQ characters or themes, according to an analysis of books posted on GranburyTexasBooks.org, a website where they have compiled parent reviews.

Lowery didn’t respond to messages requesting comment.

At her first meeting as a school board trustee on Dec. 12 — one week after the Office for Civil Rights notified the district it had opened an investigation — Lowery called for all “obscene” books to be pulled from shelves. In response, Glenn asked her to provide a list of titles so the board could discuss it at a future meeting.

“I think as a district, we do want to resolve this,” Glenn said of the library book controversy. “Speaking on behalf of every administrator in the room, and probably community members because I know there are a few of you that are ready to have this behind you, too.”

Education and legal experts said the Education Department’s decision to open an investigation in Granbury is significant because it sets up a test of a somewhat novel legal argument by the ACLU: the idea that book removals themselves can create a hostile environment for certain classes of students.

“It’s certainly the first investigation I’ve seen by the agency testing that argument in this way,” said W. Scott Lewis, a managing partner at TNG, a consulting firm that advises school districts on complying with federal civil rights laws.

The ACLU of Texas made similar legal arguments in another civil rights complaint filed last month against the Keller Independent School District in North Texas in response to a policy banning any books that mention “gender fluidity.” The Education Department has yet to decide whether to open an investigation in Keller, Kempf said.

Jonathan Friedman, the director of free expression and education at the nonprofit PEN America, which has tracked thousands of school book bans since last year, said the same legal argument could be made in districts across the country where parents, school board members and administrators have expressed anti-LGBTQ motivations.

“It’s not uncommon to see people explicitly saying that they want to remove LGBTQ books because they believe they are indoctrinating students,” said Friedman, who cited a case in Florida in which a teacher called for the removal of a children’s picture book about two male penguins because, she said, it promoted the “LGBTQ agenda.”

Granbury isn’t the only North Texas school district facing federal scrutiny.

The Office for Civil Rights over the past year has opened five investigations into allegations of discrimination at the Carroll Independent School District in Southlake, a wealthy Fort Worth suburb that has been at the center of the national political fight over the ways schools address racism, gender and sexuality. If the Education Department finds Carroll students’ rights have been violated, experts said, the federal agency could require the district to implement the same types of diversity and inclusion training programs that conservative activists have fought to block in Southlake.

Carroll Superintendent Lane Ledbetter has said the district has taken steps, including retraining staff members in how to handle bullying complaints, to ensure students from all backgrounds feel safe at school.

“If OCR determines that there are steps that we can take beyond what we have implemented, then we will absolutely comply,” Ledbetter said in a video address to the community after news of the federal civil rights investigation broke last year. “My priorities are kids, and we’re going to keep them safe.”

As in Southlake, some students and parents in Granbury say they’re counting on federal investigators to force changes.

Lou Whiting, 17, a nonbinary senior at Granbury High School, said Glenn’s recorded comments made them feel unsafe and unwelcome at school. Whiting, who helped organize student protests of the book removals, cried when they learned that the federal government had opened an investigation.

“It’s just really good to hear that there are people who are listening to us and actually doing something about it,” Whiting said. “It means a lot to hear that our efforts meant something.”