The prime minister is standing his ground on the Trans Mountain pipeline expansion as Alberta feuds with B.C. over new restrictions on shipments of bitumen that would flow through pipeline networks from Alberta to the West Coast.

"We have a federal government to look out for the national interest above various disagreements within the provinces and we did exactly that on the Trans Mountain pipeline," Justin Trudeau said in an interview Thursday with CBC Radio's Edmonton AM.

"I'm not going to opine on disagreements between the provinces in this case," said Trudeau, who is in Edmonton for a town hall meeting at MacEwan University Thursday night, part of a series of meetings in Western Canada.

"We're just going to reiterate that the decision we made was in the national interest and we're going to move forward with that decision, which means we're going to get the Trans Mountain pipeline built."

Alberta Premier Rachel Notley has threatened legal action and economic sanctions in retaliation against new spill restrictions in B.C. which would create another roadblock for the already-delayed Kinder Morgan pipeline expansion.

The $7.4-billion project was approved by the federal government in 2016.

'We can't continue to be trapped'

Trudeau said the decision was environmentally and economically sound and the new sanctions will not succeed in derailing the project.

"We know that getting our oil resources to new markets across the Pacific is absolutely essential," Trudeau said.

"We can't continue to be trapped with the price differential we have in the American market. We need this pipeline and we're going to move forward with it responsibly like I committed to."

B.C. is proposing to restrict any increase in diluted bitumen shipments while it conducts more spill response studies. Notley described the proposal as an "unconstitutional attack" and vowed to fight the policy in court.

George Heyman, B.C.'s minister of environment and climate change strategy, denied that it is sparking a constitutional crisis, saying his government is just doing its job.

They're both sort of right and they're both a little bit wrong - Eric Adams, legal expert

Eric Adams, an associate professor in the faculty of law at the University of Alberta specializing in constitutional law, said Notley's claims that B.C. is breaking federal law are only partially correct.

"They're both sort of right and they're both a little bit wrong," Adams said.

"To the extent that B.C.'s jurisdiction is interfering with the ability of the pipeline to be constructed, they're probably overreaching their constitutional jurisdiction, but to say that they have no ability to care about environmental concerns within their borders is also not right."

Legally, the dispute is not as black and white as the duelling NDP governments suggest, Adams said.

"It's a really tricky area and the lines are blurry," he said. "Which is why politicians are able to speak definitively, but on the other hand, maybe it's not as definitive as they are suggesting."

'Overlapping powers'

According to the Constitution, Ottawa has jurisdiction over federal infrastructure projects like pipelines, but B.C. has a strong legal standing over environmental threats within its borders, Adams said.

"B.C. is doing what they know they have capacity to do," he said. "Which is, make life difficult for this infrastructure project which they are opposed to, and they're going to continue to that."

'I'm not going to characterize it as a dispute between that province and this government,' says Natural Resources Min. Jim Carr. 3:19

According to constitutional law, Trudeau could pull rank and make the project expansion happen through legal sanctions, said Adams, but it's more likely that the dispute will be resolved in the courts.

"Our Constitution is one of overlapping powers and that causes difficulties and uncertainties," he said. "The governments have to be prepared to listen to one another and to work together toward a solution.

"The reason that's not possible at the moment is that they're both taking hard line positions where that compromise is not possible."

'This is not new'

The spat is just the latest rough patch in an increasingly rocky relationship between the two provincial NDP governments which stand divided on pipelines, said political analyst Paul McLoughlin.

The threats of sanctions and economic retaliation are reminiscent of a similar spat over the Northern Gateway pipeline in 2013, which resulted in frosty relations between the provinces' two standing premiers.

"In some senses, this is not new," McLoughlin said.

"This goes right back to Alison Redford and Christy Clark. And it's the same kind of negotiation that was going on, that's how it struck me ... and there's politics in all of it."