MONTREAL -- The birth of Prince George before his sister Charlotte averted the need for a major change in British tradition.

But the recent law that changed the rules of royal succession will be challenged in Quebec court beginning Monday, and could have political consequences in Canada.

The challenge could even force Ottawa to undertake a round of constitutional negotiations, say the lawyers behind the suit.

In 2011 -- while the world wondered if the firstborn of royal couple William and Kate would be a boy or a girl -- the leaders of the 16 Commonwealth countries agreed to change the succession rules to allow a girl, if she was the eldest, to take the throne.

Before the change, she would have been passed over in favour of her brother.

The Harper government implemented the change by a simple federal law in 2013.

According to Patrick Taillon and Genevieve Motard, law professors at Laval University, this was a change to Canada's constitution that should have required the consent of the provinces, which the prime minister never sought.

Now, Taillon and Motard are aiming to have the law on royal succession declared unconstitutional.

The professors have the support of Quebec's Attorney General and -- improbably -- a monarchist league, the Canadian Royal Heritage Trust.

The government argues that the modification made by the British Parliament concerning the monarchy applies automatically under Canadian law -- Ottawa had only to pass a law giving "assent," with no need for a constitutional change.

Those who are contesting the law say the British Parliament lost its right to legislate for Canada with the repatriation of the Constitution in 1982.

In an interview, Taillon said the intention of the suit is primarily "so that the Canadian Constitution is respected by the federal government."

If the law is invalidated by the court, the federal government will be faced with a choice: refuse to touch the Constitution and default on Canada's obligations to the Commonwealth, or open the Pandora's box of constitutional negotiations, where the provinces could bring their demands to the table.

According to Taillon, if the law is invalidated it could also change Quebec's balance of power on the constitutional front.

Because of obligations to the Commonwealth, the federal government would have no choice but to listen to provincial demands, unlike in the past when he says Harper abandoned Senate reform rather than seek the approval of the provinces.

"In this case, he can't say 'we won't act' because he's involved with the other countries," Taillon said, while admitting that the international consequences of doing so might not be more severe than when Canada withdrew from the Kyoto protocol.

He says the group has "nothing against the essence of the reform," referring to changing the law to allow a woman to inherit the crown.

The case is expected to last two weeks in Quebec Superior Court.