B.C. NDP Leader John Horgan says the federal government could end up having to use the notwithstanding clause to proceed with the controversial expansion of the Trans Mountain pipeline if his party wins next spring's provincial election.

"This is a project that I believe is not in the interest of British Columbia, not in the interest of our marine environment, not in the interest of our economy," Mr. Horgan said in an interview Tuesday, when asked about comments he made earlier this week suggesting the notwithstanding clause could come into play.

"I suppose they could do that, but we're a long, long way from that."

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The notwithstanding clause allows Parliament or provincial legislatures to override certain portions of the Canadian Charter of Rights and Freedoms.

The B.C. Opposition Leader's suggestion that the notwithstanding clause of the Charter could somehow factor into the pipeline debate prompted immediate ridicule from former federal cabinet minister Jason Kenney, now running for the leadership of the Alberta Progressive Conservatives, as well as skepticism from a legal expert who said the provision simply would not apply.

The New Democrats' opposition to the pipeline, and what the party might do about it if elected, is likely to become a key issue ahead of May's provincial election.

Mr. Horgan has been a vocal opponent of the Trans Mountain project, while he has been less clear about his position on other resource projects.

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Prime Minister Justin Trudeau announced the approval of Kinder Morgan's Trans Mountain expansion late last month, arguing that it is necessary for getting Alberta bitumen to Pacific Rim markets and insisting it can be done safely.

Mr. Horgan did not elaborate on his comments about the notwithstanding clause, nor did he explain in what scenario it might apply, but said he would do what he could to oppose the pipeline.

"I am going to use all of the tools available to me as leader of the opposition and, following the election in May, as premier, to protect the interests of British Columbia," he said.

Mr. Kenney quickly took to Twitter to deride Mr. Horgan and later mocked him for even thinking the B.C. government could decide on the project in the first place.

"It is clear from Mr. Horgan's comments that he does not have a flying clue about what is in the Canadian Constitution. In his ignorance he has imagined a non-existent provincial power to 'dictate' what passes through ports, which would be a total and obvious violation of how Canada has functioned as an economic union for 150 years," Mr. Kenney said in a statement.

"These comments reveal that the NDP's opposition to the approved Trans Mountain pipeline project is not based on law or facts, but a deep ideological opposition to resource development."

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But Mr. Horgan dismissed criticism from Mr. Kenney.

"Jason Kenney is seeking an office and I'll leave him to his campaigning," Mr. Horgan said. "My job is stand up for British Columbia and that's what I'm doing."

Joel Bakan, a constitutional law professor in the Peter A. Allard school of law at the University of British Columbia, said the notwithstanding clause simply cannot be used by the federal government to push through a pipeline.

In an interview Tuesday, Prof. Bakan noted the clause applies to issues around rights in the Charter, but doesn't really apply to a pipeline in any obvious context.

"It's hard for me to imagine a scenario where the federal government or Parliament would operationalize the notwithstanding clause in relation to provincial objections to the transport of bitumen by a pipeline," he said.

"The reason it's hard to imagine that is because the notwithstanding clause is used when the government wants to avoid the operation of the Charter, and the operation of the Charter has really nothing to do with decisions around whether to put a pipeline through British Columbia."

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Prof. Bakan said the only place he could see the Charter being relevant would be if the federal or provincial government wanted to suppress protesters blocking pipeline development, so passed a law saying notwithstanding freedom-of-expression aspects of the Charter, it was suspending such guarantees.

"That's the only place I can see the Charter would be relevant to the pipeline issue," Prof. Bakan said.

Prof. Bakan said the federal government may rely on what's called the constitutional paramountcy doctrine to push through the pipeline over provincial objections, but the province would have a good argument against Ottawa.

B.C. Premier Christy Clark, whose Liberals will be seeking a fifth consecutive term in next year's election, has signalled a willingness to support the project, subject to proponents meeting five conditions that include an effective spills response and a fair share of economic benefits from the project for British Columbia.