The Dallas Stars fired head coach Jim Montgomery on Tuesday due to what the team’s general manager says was “unprofessional conduct.”

GM Jim Nill says he was made aware of the situation on Sunday in a phone call

“This decision was made due to unprofessional conduct inconsistent with the core values and beliefs of the Dallas Stars and the National Hockey League,” Nill said in a statement on Tuesday.

Nill declined to discuss the act that led to Montgomery’s firing during a press conference on Tuesday afternoon saying he wouldn’t comment out of respect to those involved. He did specify the act wasn’t criminal and has no connection to players past or present that the organization is aware of.

He said ownership, general counsel and management were all involved in the process and no other employees were impacted by Montgomery’s act. Nill added it was a “very tough decision.”

“I have a lot of respect for Jim Montgomery. He’s a very good coach,” Nill said. “Unfortunately, sometimes in life, the hardest decisions are the toughest and this is one of them.”