Montreal Mayor Denis Coderre announced the city's official opposition to proposed Energy East pipeline project Thursday, saying the potential risks outweigh its possible economic benefits to communities including his.

Coderre was joined by mayors from neighbouring cities including Laval and Longueuil that make up the Montreal Metropolitan Community.

"We are against it because it still represents significant environmental threats and too few economic benefits for greater Montreal," said Coderre on behalf of the MMC.

The announcement follows 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.

A report based on the consultations recommended the MMC oppose the Energy East project.

"It was perhaps no surprise that environmental concerns were the most prominent theme," Coderre said, highlighting worries for drinking water and other risks related to a potential oil spill.

Coderre said the economic ramifications of a potential spill also factored into the decision. Whereas the economic returns of the pipeline have been pinned at $2 million a year, he put the cost of cleaning up a spill at between $1 billion and $10 billion.

All in all, Coderre said the Energy East project has potential social, economic, environmental and public security impacts that cannot be tolerated.

TransCanada will 'continue to consult'

The City of Montreal's official opposition is the latest challenge to TransCanada Corp.'s proposed pipeline project, which would carry 1.1 million barrels a day of oilsands crude through Quebec to an export terminal in Saint John, N.B.

The project would include the existing TransCanada pipeline as far east as Montreal plus a new pipeline through Quebec.

TransCanada Energy East pipeline

TransCanada's proposed Energy East pipeline would ship crude from Alberta to New Brunswick. (Canadian Press)

Coderre has voiced concerns about the project in the past, but until now has not taken an official position on it.

Laval Mayor Marc Demers said in September that he is "firmly against" the proposed pipeline.

Earlier Thursday, Energy East spokesman Tim Duboyce said the company will wait to see precisely what the mayors have to say and take it from there. 

"We see this as an opportunity to have a document to help lay out what those concerns are so we can continue to consult with elected officials and other stakeholders," he said.

Wildrose Party questions numbers, condemns 'hypocrisy'

In a statement, Brian Jean, leader of Alberta's Wildrose Party, called Coderre's position "disgraceful."

"While Mr. Coderre dumps a billion litres of raw sewage directly into his waterways and benefits from billions in equalization payments, his opposition to the Energy East pipeline is nothing short of hypocritical," Jean said.

Jean claimed the project would entail economic benefits of $9.2 billion for Quebec, citing numbers provided by TransCanada.