Justin Trudeau has pressed one of the hottest issue buttons in Quebec, saying there's no need to toughen the province's language laws.

During a visit to Quebec City on Thursday, the Liberal leadership candidate was asked by reporters about plans by the Parti Québécois provincial government to toughen so-called Bill 101, Quebec's French-language charter.

The pro-independence PQ calls the matter urgent, following census data that suggests a decline in francophones' demographic weight in the province.

Trudeau's response: The PQ language policy is unnecessary and counter-productive.

While he expressed support for the old Bill 101, pointing out that it has allowed French to thrive in a Quebec nestled in a bilingual Canada, Trudeau said Thursday that adding teeth now to the language law risks needlessly reigniting old battles.

"I think we are revisiting old debates," Trudeau said.

"The majority of people in Papineau" — his Montreal riding — "in Quebec City and across Quebec are focused on their jobs, the economy, health and education of their children to participate fully in this era of globalization in which we live."

'Lack of knowledge'

The PQ's reaction was swift. Jean-François Lisée, Quebec's minister for la Francophonie, said Trudeau doesn't know what he's talking about.

Quebec's minister for la Francophonie, Jean-François Lisée, says Trudeau doesn't grasp the basic issue. (Jacques Boissinot/Canadian Press)

"Well, I'm a bit disappointed by the lack of knowledge that he shows of the basic issue. So I'm asking him and others who don't see the problem, when will it become a problem?" Lisée said.

The provincial government has decried census data released this week that showed a drop in the proportion of Montrealers whose mother tongue is French, to well below 50 per cent. In the greater Montreal area, 64.5 per cent of people declared French as their native language, down from 65.7 per cent in the 2006 census.

Lisée said it's deplorable that francophones are leaving Quebec's largest city.

"To speak of a Montreal that's majority francophone is a legitimate goal," he said.

Echoes of father Pierre

But Trudeau isn't alarmed by the new census figures, saying it is the result of demographics and a lower birthrate.

"My concern about reinforcing Bill 101 is that we will find it punishes Quebec francophones who want their children to develop a capacity in English, the language of international commerce," he said. "I don't think this is a good direction."

He also suggested that French is faring better than it used to in Quebec. Trudeau pointed out that while older immigrants may speak their native language and English, their children are becoming fluent in French.

"If I speak to the parents of people from Bangladesh, Pakistan or India, yes, the parents speak English. But when I speak to the children of five, 10 or 15 years old in my riding, they're speaking French, and it's because Bill 101 works."

Trudeau's opinion on language to a certain extent echoes the position of his father, former prime minister Pierre Elliott Trudeau, who brought official bilingualism to Canada and criticized the French-only policies of the PQ.

With files from CBC News