A pair of Quebec professors is challenging Canada's approval of new royal succession laws that say a first-born child, regardless of gender, can now inherit the throne.

Canada adopted the Succession to the Throne Act in March, as did the 16 other Commonwealth countries which still consider the queen to be their head of state.

The move was in support of a bill adopted in British Parliament in April, aimed at modernizing the rules of succession that previously stipulated a younger male child could leapfrog his older sister to take the throne.

Under the new rules, the first-born child of Prince William and the Duchess of Cambridge, due sometime next month, will be heir to the throne regardless of whether it is a boy or a girl.

But last week the Quebec professors said Ottawa's decision to approve the act without seeking the support of all the provinces is contrary to Canada's Charter of Rights and Freedoms.

"In the other federation involved in the Commonwealth, which is Australia, the consent of all six member states is sought and obtained by the federal government before the federal government adopts its legislation on royal succession. So, we say the same rule applies in Canada," Andre Binette, one of two Quebec lawyers representing the professors, told CTV’s Canada AM.

"Because the Constitution says all laws relating to the office of the queen or the monarchy must be adopted following a constitutional amending procedure that requires the unanimous consent of all the provinces plus the federal parliament."

Quebec's provincial government was invited to take part in the legal fight, but decided to stay out of it, Binette said.

Laval University professors Genevieve Motard and Patrick Taillon filed the case in the province’s Superior Court last week.

In addition to claiming the government acted unconstitutionally, they say the new succession laws would still prevent a Roman Catholic from becoming king or queen -- another bone of contention with the archaic succession laws that they say hasn't been properly addressed.

Binette, who was legal counsel to the Quebec government during the 1995 referendum on sovereignty, said Quebec already has a challenge lodged in the Supreme Court related to provincial involvement in Senate reform. That challenge also involves the Constitution Act of 1982.

"So there will be a major constitutional decision by the Supreme Court on the Senate, which in my view will lead to the same conclusion -- that provincial consent is necessary before Senate reform is possible. If you add that to this case on the monarchy I think we're headed towards major constitutional negotiations," Binette said.

He acknowledged that the new legal challenge against the Succession to the Throne Act isn't about wanting to prevent first-born daughters from becoming monarch, but rather about re-opening the debate over the Constitution.

"It's about the legal status of the monarchy in Canadian law under the Constitution of 1982 and ultimately it's about Canadian independence from the United Kingdom," Binette said. "So the issue here is whether the laws relating to the monarchy are a part of Canadian law or not."