The leader of B.C.'s apparent government-in-waiting has upped the ante in his push against the proposed Northern Gateway project, vowing to pull B.C. out of the federal review process if he's elected next spring, while also considering a legal challenge on who has jurisdiction over pipelines.

Adrian Dix – whose B.C. New Democrats have opened up a consistently wide lead over Premier Christy Clark's Liberals ahead of the May election – said Wednesday that if he takes office, he'll launch a B.C. environmental assessment that, unlike the federal review, protects the province's interests.

The announcement represents Mr. Dix's sharpest words yet against the $6-billion twin Enbridge pipelines that would run from Alberta to the coastal B.C. community of Kitimat. Mr. Dix has repeatedly said Northern Gateway is not in B.C.'s best interest and his staunch opposition might well trigger political and economic consequences that go beyond the province's border.

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"If we do nothing, then the decision of the B.C. government will be made by [Prime Minister] Stephen Harper. I don't think that's acceptable to British Columbians. I think the people of B.C. want people in B.C. to have a voice in that process and we intend to provide that," Mr. Dix told reporters during a news conference in downtown Vancouver, flanked by his party's environment critic and constitutional lawyer Murray Rankin.

Mr. Dix – who has been at his party's helm since April of last year – said an equivalency agreement signed by the province and Ottawa in 2010 allows either party to withdraw from the review process with 30 days written notice. He said he would serve notice within a week of taking office, though he disputed the assertion he was making the election a referendum on Northern Gateway. He said he "would love" if the current B.C. government dropped out of the review process itself.

Questions remain, however, on what the province could do to stop a project that appears to be under federal jurisdiction. When asked if B.C. could legally block Northern Gateway, Mr. Rankin suggested it's possible, though there's little case law to draw from.

"The primary jurisdiction over an interprovincial pipeline is federal. That does not mean, however, that there isn't a number of provincial powers that could come into play in a circumstance like this," Mr. Rankin said.

Though environmental groups hailed Mr. Dix for championing a B.C. environmental assessment, the province's Premier accused him of playing politics. Speaking with reporters after an event on Vancouver Island, Ms. Clark said she didn't understand how a separate B.C. assessment would benefit the province. Ms. Clark's government last month said five conditions – including a larger chunk of revenue – would have to be met for Northern Gateway to proceed.

Terry Lake, Ms. Clark's environment minister, said as long as an environmental process is thorough, one is enough. He said he feared Mr. Dix's stand would scare away investment and questioned the point of the B.C. assessment if Mr. Dix has already spoken out against the project.

Joe Oliver, federal Minister of Natural Resources, did not directly address Mr. Dix's announcement in an e-mail statement Wednesday.

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What effect Mr. Dix's decision to potentially pull out of the review process has on Alberta – and Enbridge – remains to be seen. Alberta Premier Alison Redford and Ms. Clark have clashed over the B.C. Premier's push for more revenue. Several messages left for Ms. Redford on Wednesday were not returned.

An Enbridge spokesman said the company had no response to Mr. Dix's announcement. The spokesman noted the company is about to start a four-month public review that will detail its application.

Mr. Dix was asked during the news conference if he feared his position would sour B.C.'s relationship with Ottawa. He said: "It's my intention to have a business-like relationship with whoever is Prime Minister, whether that's Mr. Harper or Mr. [federal NDP Leader Thomas] Mulcair