MANKATO (AP) — A Minnesota college football coach who was cleared of child porn charges is fighting a suspension, his union said Thursday, although neither it nor the university would say what prompted the punishment or shed light on his prospects for reinstatement.

Coach Todd Hoffner received a written notice from Minnesota State University, Mankato late Tuesday afternoon about a 20-day unpaid suspension that begins Jan. 7, the general counsel for the Inter Faculty Organization said in an email to The Associated Press. Connie Howard said the union has filed a grievance challenging the suspension.

Hoffner was put on paid administrative leave after videos of his naked children were found on his university-issued cellphone in August. A judge ruled Nov. 30 that the videos were not pornographic and dismissed the felony charges against Hoffner, accepting his testimony that the videos merely showed his children acting silly after a bath.

“The grievance charges that the university failed to follow progressive discipline and did not have just cause to issue the suspension,” Howard wrote. She declined to provide further details and would not say what reason the university gave for Hoffner’s suspension, whether it was related to the videos or what his prospects might be for being reinstated as head coach of the Mavericks.

The MnSCU system has a policy prohibiting the use of university-issued cellphones or mobile devices for personal business.

Hoffner was beginning a new four-year contract when he was escorted off a practice field in August, a few days after he returned his malfunctioning phone to the school. University technicians found the videos and notified university officials, who contacted police. Hoffner was not allowed back and had to miss the Mavericks’ 13-1 season, including their appearance in the NCAA Division II semifinals Dec. 8. He had a 34-13 record in his first four years at Mankato.

Minnesota State issued a brief statement Wednesday night saying Hoffner’s administrative leave ended Monday and he remains on the university’s payroll, but Aaron Keen remains acting coach.

“One complaint against the football coach was investigated and the investigation has been completed. One complaint against Mr. Hoffner is pending and is under investigation,” the statement said without elaboration.

University spokesman Dan Benson, citing privacy laws, told the AP he couldn’t comment on the nature of the complaints.

“The word ‘reinstated’ would not be accurate,” Benson said. “He is no longer on leave. He remains on the payroll … but he has not assumed duties as the head football coach again at this time.”

Hoffner could not be reached immediately for comment Thursday. He does not have a listed phone number. His civil attorney, Chris Madel, was in court and unavailable Thursday. His attorney for the criminal case, Jim Fleming, said he was not directly involved in the personnel case.

Minnesota State athletics director Kevin Buisman did not immediately return a call seeking comment Thursday.