OMAHA, Neb. (AP) — The University of Nebraska is asking three Republican candidates for governor to stop using its logos and other imagery in campaign ads.

The university sent letters to Charles Herbster, state Sen. Brett Lindstrom and University of Nebraska Regent Jim Pillen, according to the Omaha World-Herald.

University spokeswoman Melissa Lee said the letter was sent partly to avoid the perception that the university is endorsing a candidate.

“We understand all Nebraskans have an affinity for the red N, but university logos, slogans and other materials are trademarks belonging to the University of Nebraska, and we have a legal responsibility to protect them,” Lee said in a statement. “It is not uncommon for us to respectfully request that our trademarks not be used, including in political campaigns in which we are neutral.”

As a tax-exempt government entity, the university is barred from participating in political campaigns or endorsing candidates.

Pillen and Lindstrom both are former Husker football players. Each has highlighted that experience in ads that feature easily recognizable university logos. Herbster, the owner of multiple businesses, used university imagery in a recent ad that targets Pillen with allegations about his record on critical race theory.

Critical race theory is an academic framework generally taught to graduate students, but opponents often use the term to cover a broad range of anti-racism and diversity curriculum and initiatives.

The Herbster ad references the University of Nebraska-Lincoln’s Office of Diversity and Inclusion without using the department’s name. It uses the image of Marco Barker, the vice chancellor who leads that office. University officials said the photo of Barker is an official university image, and using it violates the university’s copyright. The letter said Barker has a right to privacy under state law.

The Herbster campaign pushed back against the letter on Monday, alleging that the univrsity “does not want to be exposed in its support of critical race theory and all the other terrible liberal policies that Jim Pillen has supported.”

The Lindstrom and Pillen campaigns did not immediately respond to requests for comment.

Lee, the university spokeswoman, said in an email Monday that the university had not determined next steps if candidates don’t take the requested actions.