CALGARY -- Opponents of the Trans Mountain pipeline expansion have no power to stop it, Alberta Premier Rachel Notley said Tuesday in her strongest rebuke yet since the outcome of the British Columbia election cast doubt over the project.

"We understand that some oppose the twinning of the pipeline and I respect their opinions," Notley told a news conference in Edmonton.

"But I fundamentally disagree with the view that one province or even one region can hold hostage the economy of another province, or in this case, the economy of our entire country."

A week ago, Christy Clark's Liberals came out of the B.C. election one seat shy of a majority government, though recounts and absentee ballots could change the outcome.

B.C.'s NDP, which promised to use "every tool in the tool box" to stop the Kinder Morgan project, won 41 seats. That leaves the Greens, which also oppose the development, holding the balance of power with three seats.

"It's our view that there are no tools available for a province to overturn or otherwise block a federal government decision to approve a project that is in the larger national interest," Notley said.

"If there were such tools, Canada would be less a country and more a combination of individual fiefdoms, fighting with each other for advantage."

The NDP premier's comments came a day after the Federal Court of Appeal granted Alberta intervener status in a lawsuit filed by municipalities and First Nations against the Trans Mountain project.

Notley said her government will make the case that it has taken measures to reduce the environmental effects of the oil and gas industry and that it's important for the country that the project go forward.

Both the City of Vancouver and the City of Burnaby, along with numerous First Nations and two advocacy groups, have filed what is now a combined lawsuit expected to be heard in October.

They oppose the project over concerns of a tanker or pipeline leak, the consequences increased tanker traffic would have on marine life and the higher upstream emissions of petroleum from the oilsands.

The Tsleil-Waututh Nation, one of the applicants of the lawsuit, opposed Alberta's intervener status.

Construction on the Trans Mountain expansion is expected to begin in September, though it still needs a final investment decision.