More than 80 mayors in the Montreal area have declared their opposition to TransCanada's proposed Energy East pipeline.

The Communauté métropolitaine de Montréal — headed by Montreal Mayor Denis Coderre — came out against the pipeline at a news conference on Thursday.

Pipeline supporters, including Calgary Mayor Naheed Nenshi​, accused Coderre and his allies of over-stating the dangers of the project. 

But do the Montreal-area mayors have the legal power to prevent a pipeline from being built in their municipalities?

The Constitution Act of 1867 stipulates that the environment is a shared responsibility of provincial and federal governments.

When a pipeline crosses a provincial boundary, however, Ottawa claims sole jurisdiction through the National Energy Board.

Municipalities and provincial governments can lobby their federal counterparts, but it is the feds who have final say about whether a pipeline gets built.

At the same time, any decision by the National Energy Board can be appealed before the courts.

Legal considerations aside, the MMC represents more than four million residents. They can, therefore, influence what might be called the "social acceptability" of the TransCanada project.

The announcement followed extensive public consultations organized by the MMC last fall that received 143 written submissions and heard 66 oral presentations. Another 3,846 people responded to an online questionnaire.

Map of Energy East

TransCanada Corp.'s proposed pipeline project, which would carry 1.1 million barrels a day from Alberta through Quebec to an export terminal in Saint John, N.B. (Canadian Press)

with files from Radio-Canada's Denis-Martin Chabot