However, the police force denied allegations its undercover officers were there on Monday to provoke the crowd and instigate violence.
Police said the three undercover officers were only at the protest to locate and identify non-peaceful protesters in order to prevent any incidents.
Police came under fire Tuesday, when a video surfaced on YouTube that appeared to show three plainclothes police officers at the protest with bandanas across their faces. One of the men was carrying a rock.
The Quebec provincial police will not comment any further on the affair, a spokeswoman in Montreal said. Quebec Justice Minister Jacques Dupuis was made aware of the news, but a spokesman from his office said he will not comment on the matter either.
What are your views on the police statement that officers acted "within their mandate to keep order and security"?