The legal battle over the carbon tax will soon reach Canada's highest court with Saskatchewan playing a major role — and a lower court ruling on Monday has increased the drama.

On Monday, the Alberta Court of Appeal ruled the federal carbon tax to be unconstitutional in a 4 to 1 decision.

Two rulings from Saskatchewan (3-2) and Ontario (4-1) went in favour of the federal government's position.

Both Saskatchewan Premier Scott Moe and Alberta Premier Jason Kenney were claiming the Alberta ruling as a victory for their case against the federal government's federal carbon pricing system.

The ruling sets the stage for next month's Supreme Court of Canada hearing. Canada's highest court will hear the cases of Saskatchewan and Ontario.

'It's the longest judgment I have ever seen'

"It will be a good court fight for sure. And it's not an easy case for the Supreme Court to decide," said John Whyte, a constitutional law expert at the University of Regina.

"There are 228 pages, 857 paragraphs. It's the longest judgment I have ever seen and it is well-argued, very well-argued, very precisely argued and makes as strong a case as ever possible for the invalidity of the carbon tax," Whyte said.

"I thought that the federal case was not a slam dunk but strong. But four judges going with the provincial claim of unconstitutionality was a little surprising," Whyte said.

Whyte said his "hunch" was that the top court would mirror the Saskatchewan Court of Appeal split decision.

"It's anything but an open and shut case."

Carbon tax a 'constitutional Trojan horse'

The Supreme Court of Canada chose not to wait until after the Alberta decision was rendered to set its hearing for Saskatchewan and Ontario, but that does not mean the Alberta ruling will be set aside.

The Alberta decision "is going to have an impact on the upcoming Supreme Court of Canada hearing no doubt," said Dwight Newman, constitutional law professor at the University of Saskatchewan.

The 4-1 Alberta decision rejected Ottawa's argument that regulation of greenhouse gas emissions is an issue of national concern, citing the division of powers in the constitution that gives the provinces responsibility for non-renewable resources.

The majority opinion called the Greenhouse Gas Pollution Pricing Act "a constitutional Trojan horse."

Newman said the majority of Alberta justices concluded that if the legislation stood it will "greatly expand the powers of the federal government. What they've called, in this very memorable phrase, a constitutional Trojan horse."

Premiers renew call to cancel tax

Alberta Premier Jason Kenney said the court ruling should force the federal government to cancel the tax in his province.

Newman said that argument can be made.

"Based on this decision there is a basis to say that in Alberta the determination of the law at this point is that the tax is indeed illegal."

On Monday, Moe said the federal government should cancel the tax pending the highest court's decision.

"We would ask that the Trudeau government pull the carbon tax off of Canadians here and re-engage with Canadians in a much more collaborative manner," Moe said Monday.

Federal Environment Minister Johnathan Wilkinson said he is confident in Ottawa's position.

"We look forward to the Supreme Court which is the ultimate arbiter of issues around differing interpretations of jurisdiction to be making the ultimate determination in March," Wilkinson said.