NHL commissioner Gary Bettman upheld Shawn Thornton's 15-game suspension, he announced in a 12-page ruling on Tuesday.
The suspension had been issued following Thornton's attack on Pittsburgh's Brooks Orpik in a game on Dec. 7 that resulted in a concussion for the Penguins defenseman.
Thornton had an appeal hearing with the NHL on Friday and since then has been awaiting a written ruling from Bettman.
"Simply put, this was a bad act with a bad result, and neither will be tolerated in our game," Bettman wrote. "Again, I note that Mr. Thornton has a reputation for being a 'good actor' and a model NHL citizen, but that does not eliminate the need for him to be punished appropriately for his bad act in this case."
Bruins GM Peter Chiarelli released a statement hours after the announcement was made.
"We respect the process including the ability to attend the hearing with Commissioner Bettman in support of Shawn. At this time, we will decline comment until the process is complete and Shawn has exhausted all rights available to him."
Thornton may appeal his suspension once again through a neutral arbitrator.
After the incident between Thornton and Orpik, Thornton was ejected and suspended indefinitely. He was then given a 15-game suspension from NHL senior vice president of player safety Brendan Shanahan a week later.