Update 9:20 a.m. April 18 – The province announced it will file the reference case in B.C.’s highest court by April 30.

In the ongoing pipeline battle between B.C. and Alberta, politicians on both sides have been accused of flouting Canada's Constitution – but is there any truth to the rhetoric?

According to Joel Bakan, a constitutional expert and law professor, the answer is fairly black-and-white: B.C. hasn't breached the Constitution, and Alberta's proposal to throttle outgoing fuel shipments certainly would.

"The B.C. government is acting perfectly within its rights, and appropriately, and what the Alberta government is doing is a flagrant breach," said Bakan, who teaches at the University of British Columbia's Peter A. Allard School of Law.

B.C. is currently preparing a reference case to clarify whether it has the right to restrict diluted bitumen shipments to its coast on environmental grounds – in essence, seeking an answer to a constitutional question that could have wide-ranging impacts.

It appears to have made Kinder Morgan anxious about the future of its Trans Mountain pipeline expansion, at least enough for the company to suspend non-essential spending until it can receive assurances the project will be able to move forward unimpeded.

But given B.C.'s position, Bakan said seeking clarification from the court is an entirely valid course of action.

"Even though the pipeline is a federal undertaking, the Supreme Court of Canada has consistently said that there is a place for even quite robust provincial regulations, so long as it doesn't impair the operations of the pipeline," he told CTV News from London.

By contrast, Bakan said the law Alberta tabled on Monday, which would give the province the power to dictate how much fuel can be shipped outside its borders, clearly violates Section 91(2) of the Constitution.

It also goes against established precedents; Bakan said the Supreme Court of Canada delivered decisive rulings against these kinds of actions in the 1970s when provinces were squabbling over pork and eggs.

"There was a big food fight, pardon me, between Manitoba and Ontario," he said. "And the cases that were decided are basically the precedent that suggests that what Alberta's doing is unconstitutional."

While many British Columbians have become nervous that Alberta's law would drive up already painfully steep gas prices, Bakan said if it's ever passed, the legislation is almost certain to be challenged in court.

It's unclear whether the province would ever actually follow through with the threat, however. On Tuesday, B.C.'s Attorney General, David Eby, called the legislation "a bluff" and said his government wouldn't hesitate to fight back – through the proper legal channels.

"If they did use it, we'd be in court immediately," Eby said.

Ironically, while Alberta Premier Rachel Notley claims to be acting in defence of the province's oil industry, Bakan said it's possible an Alberta company would launch its own challenge against the law, should it be ordered to limit shipments to B.C. and hurt its bottom line.

With files from CTV Vancouver's Bhinder Sajan