HALIFAX - Nova Scotia and Newfoundland could score political points at home by suing Ottawa over the Atlantic Accord offshore energy deals, but winning the case would be a long shot, says an expert in constitutional law.

Wayne MacKay, a law professor at Dalhousie University in Halifax, says the courts would likely agree to hear the case, based on the fact that the 2005 agreements have legislative clout.

But the courts are just as likely to conclude that the dispute, which centres on whether Ottawa is breaking the agreements, belongs in the political arena because of the constitutional supremacy of parliament.

"It may be a good political tactic in terms of putting pressure on and showing the province is serious,'' said MacKay."(But) I think there's a pretty high possibility of (the case being tossed out) because ... supremacy of parliament is still a pretty strong principle in Canada.''

Both Newfoundland Premier Danny Williams and Nova Scotia Premier Rodney MacDonald maintain the federal Conservatives have broken a promise to respect the accords, which protect their offshore oil and gas revenue from being clawed back under the federal equalization program.

But Ottawa has vehemently denied the allegation, stressing that the March 19 budget gives the provinces the choice of opting into a new equalization formula or sticking with the current arrangement.

The back-and-forth over the issue prompted Prime Minister Stephen Harper to challenge the provinces to sue, an option Saskatchewan Premier Lorne Calvert has decided to explore.

Calvert is upset that non-renewable resources have not been excluded from the new equalization formula contained in the budget.

Calvert has said the Conservatives broke a key campaign pledge and the province will mount a legal challenge under the Constitution, arguing that Saskatchewan is being treated unfairly by the equalization program.

"If it's proceeded with, it would be a reference to the Saskatchewan Court of Appeal, based on breaches of constitutional duties that lie on the federal government,'' said John White, a constitutional law expert with the Saskatchewan Institute of Public Policy.

"It wouldn't be based on notions of betrayal or anything else, just a fairly straightforward constitutional argument.''

White said Saskatchewan's plan of attack arises from recognition there appears to be no other option.

"The preferred way of conducting federal-provincial relations through meeting and negotiation has lost its currency, at least with respect to the Conservative government of Canada and the NDP government of Saskatchewan,'' he said.

By contrast, there seems to enough goodwill for negotiations to continue between Nova Scotia and Ottawa over some sort of "insurance policy'' that would ensure the province will be no worse off no matter what option it chooses.

And while the premiers of Nova Scotia and Newfoundland said last week they were not ruling out joining Saskatchewan in its court challenge, both appear reluctant to go to court.

Meanwhile, Nova Scotia expanded an ad campaign Monday across the country encouraging Canadians to sign an online petition to get Ottawa to honour its signed agreement.

MacDonald's office confirmed Monday it had received 3,600 responses as of midday.