The team did not elaborate on the conduct in its statement.
“The Dallas Stars expect all of our employees to act with integrity and exhibit professional behavior while working for and representing our organization,” Stars general manager Jim Nill said in the statement. “This decision was made due to unprofessional conduct inconsistent with the core values and beliefs of the Dallas Stars and the National Hockey League.”
The 50-year-old Montgomery was in his second season with the Stars after five seasons as coach of the University of Denver. He has two years left on his contract at $1.6 million per season.
Dallas finished fourth in the Central Division last season but made a run in the playoffs, losing in seven games in the second round to the eventual champion St. Louis Blues.
The Stars, who are currently fourth in the division, host New Jersey on Tuesday night.
The Stars said that assistant Rick Bowness will take over as interim coach, with Texas Stars (AHL) head coach Derek Laxdal joining his staff. Texas Stars assistant Neil Graham will take over for Laxdal.