The league announced Wednesday it fined the Impact and coach Marco Schallibaum after players swarmed referee Jorge Gonzalez during a 3-0 loss to the Vancouver Whitecaps.
Schallibaum, who has been suspended four times for a total of five games in his first year with Montreal, was fined $2,000. The club was fined $10,000 because it violated the league's mass confrontation policy for a third time.
Vancouver received an official warning for their first violation of the season.
Players from both teams were livid after Gonzalez pointed to the penalty spot after what appeared to be a hand ball by Vancouver Jun Marques Davidson in the 38th minute of the game on Saturday, but then reversed his decision after consulting the fourth official.
Coincidentally, Impact sporting director Nick De Santis was serving a one-game suspension for confronting an official after a match the previous week against Columbus.
The league also fined Chivas USA defender Mario De Luna an undisclosed amount for kicking out at Houston Dynamo kidfielder Brad Davis. No foul was called on the play in the 44th minute of thier match on Saturday.
De Luna was suspended one game in May for shoving a ball boy during a game in Portland.