The Harper government is intervening in a court case that seeks to invalidate Bill 99, the provincial law passed 13 years ago asserting Quebecers' right to decide the rules of secession from Canada.

The Attorney General of Canada filed a declaration of intervention in Quebec Superior Court on Wednesday, while the media's attention was focused on the throne speech in Ottawa. It was brought to the public's attention by Maclean's magazine on Friday.

The government of former Parti Québécois premier Lucien Bouchard passed Bill 99 back in 2000 in response to the federal government's Clarity Act, which set out the conditions under which Parliament would negotiate with Quebec to secede.

The provincial law's legality was challenged by Keith Henderson, the last leader of the long-defunct anglophone rights party, the Equality Party. It's taken 13 years to get on the court docket. The case is expected to be heard sometime in 2014.

"We felt it was unconstitutional. We challenged it and we were hoping the federal government would participate," said Brent Tyler, the lawyer who filed the original challenge against Bill 99.

"It wasn't until just recently, last Wednesday, that the federal government of Canada under Stephen Harper's conservatives decided to intervene in our favour. Our view is better late than never"

The federal Attorney General is intervening in the case to challenge several aspects of the law, notably that 50 per cent plus one vote would be enough to trigger negotiations on Quebec's independence.

Not reopening constitutional debate, Harper spokesman says

Shortly after the Conservatives came to power in Ottawa in 2006, the prime minister passed a motion recognizing the "Québécois as a nation within a united Canada."

It's the first time since then that the federal government has waded into the constitutional battle.

However, in an email sent to Radio-Canada today, the Prime Minister's Office said it had "no intention of reopening the constitutional debate."

"The traditional position of the government of Canada in this litigation is well known," said the prime minister's spokesman, Carl Vallée, in the email. "Given that this matter is before the courts, we cannot comment any further."

Others are commenting, however.

"By addressing Bill 99, passed by the National Assembly, the federal government directly attacks the right of Quebec to decide its future," said Bloc Québécois leader Daniel Paillé, in a statement.

Quebec Intergovernmental Affairs Minister Alexandre Cloutier tweeted his disappointment that the federal government "is trying once again to deny Quebecers the right to alone decide their political future."