Three people were arrested late Thursday afternoon for allegedly assaulting police officers at a demonstration against  a controversial plan by Enbridge to reverse the flow of oil in the Line Nine pipeline from Sarnia, Ont. to Montreal.

Twenty-nine others, including one minor, faced penalties under the provisions of Montreal's controversial bylaw P6 — the municipal bylaw setting out rules for public demonstrations.

The protest near Montreal's Victoria Square coincided with the third day of National Energy Board hearings into the proposal taking place nearby at the Palais des Congrès.

Montreal police declared the demonstration illegal at around 4 p.m. and dispersed the protesters.  The demonstration was over by about 6 p.m.

Opponents say pipeline poses huge risks

On Tuesday, the first day of hearings into the Enbridge proposal, about 15 protesters were expelled from the conference room after disrupting the proceedings.

The project's opponents say they believe the project poses significant risks to communities along the corridor between Sarnia and Montreal.

If approved, the pipeline will be allowed to carry heavy crude originating in Alberta to eastern Canada.

Opponents worry about the impact of a potential oil spill near Lake Ontario and the St. Lawrence River or on valuable agricultural land.

Enbridge: economic benefits outweigh risks     

Enbridge argues the project would provide refineries in Quebec and Ontario with a more secure oil supply from Western Canada, at a lower price than foreign imports.

Quebec Premier Pauline Marois has agreed to create working groups to look into the economic benefits and environmental risks of the pipeline project.

She, too, has said it could be a boon for the province, producing jobs and boosting tax revenues.