The Canadiens appeared to score with about two seconds remaining in the third period to take a 5-4 lead, but the NHL's Situation Room initiated a goaltender interference review and nixed the goal. The game ultimately went to overtime, and the Senators won in a shootout.
The league explained postgame that Gallagher "impaired Ottawa goaltender Matt Murray's ability to play his position in the crease prior to the puck entering the net."
Gallagher disagreed with that assessment.
"I get knocked on my ass - I have time to reset, you can't tell me the goalie doesn't have time to reset," the Canadiens forward said, according to Sportsnet's Eric Engels.
Gallagher added that the NHL shows teams a video depicting goaltender interference every season, and he saw one in which Toronto Maple Leafs netminder Frederik Andersen got pushed but was able to recover, so the goal stood. Gallagher said the officials received the same video.
The veteran forward believes the inconsistency in rulings on video reviews has had a negative effect on the sport.
"To me, it's ruined the product," he said, according to The Athletic's Arpon Basu.
Tuesday's disallowed goal was the second controversial ruling impacting the Canadiens in a span of three days. On Saturday night, a Montreal goal that cut the Maple Leafs' lead to 4-3 in the second period was initially upheld. However, the Leafs then challenged the play for goalie interference, and the goal was overturned. Toronto won that contest 5-3.
Canadiens head coach Claude Julien could not use his coach's challenge because reviews in the final minute of regulation and overtime are handled by NHL Situation Room in Toronto.