Facing a public backlash and possible legal action, the Conservatives have decided to add linguistic questions to the short-form census and drop the threat of jail time for those who refuse to participate.

Industry Minister Tony Clement said Wednesday that three linguistic questions will be included.

An Ottawa group had issued a legal challenge to the government to block the National Household Survey from replacing the long-form census, arguing the census is crucial to the delivery of French-language services. The Federal Court agreed to fast-track the case and set a hearing date for Sept. 27-28.

Clement said the latest changes "will ensure the government's compliance with the Charter of Rights and Freedoms, Official Languages Act and its regulations."

"Our government believes that this fair and reasonable approach is a better balance between collecting necessary data and protecting the privacy rights of Canadians," Clement said.

Liberal MP Bob Rae said Clement is "scrambling" to answer those who are critical of the government's move to a voluntary survey.

"Everyone agrees that we don't need prison sentences to have a mandatory form. We do need a mandatory long-form to be able to provide reliable data to the provinces and to the people of Canada about the condition of the Canadian people, about how we're doing," Rae told CTV News Channel early Wednesday evening.

"The language issue is now in a compulsory form. But the question will then be, ‘What about the other questions?' I just think the minister doesn't have a logical answer to any of these questions."

Earlier Wednesday, the former head of Statistics Canada, in a last ditch effort to dissuade the government from abandoning the mandatory long-from census, said the move will imperil the reliability of information collected by the agency across the board.

Data from the long-form census "provides the benchmarking" for many of the surveys that StatsCan conducts, Munir Sheikh said.

"If we don't have that benchmarking available we will not be able to tell whether or not the data we are conducting from other surveys is truly reliable or not," he told CTV's Canada AM. "Without that reference point we can't really tell whether that information is good or bad."

Sheikh resigned from his post as the agency's top statistician last month after media reports, quoting Clement, reported that StatsCan recommended Ottawa replace the mandatory long-form census with a voluntary survey.

Clement has since distanced himself from those comments.

Yesterday, the government released nearly 200 pages of emails and briefing notes to the House of Commons Industry committee, which is probing the government's decision to scrap the mandatory long-form census and replace it with the voluntary National Household Survey.

The documents reveal that just before Sheikh resigned he was set to tell agency staffers that the National Household Survey, "will not provide useful data" to groups that use the mandatory long-form census.

However, that meeting was cancelled and Sheikh resigned hours after the government was made aware of his proposed comments, according to the newly released documents.

Sheikh would not comment on whether the Conservatives were trying to control what the agency said about the census change, saying that he would "let the documents speak for themselves."

"The information that has been made public, I think people can read that information and draw their conclusions from it," he said Wednesday morning, adding that he stands by his decision to leave his post.

Dropping the mandatory long-form survey has been widely criticized and experts say the data will be virtually useless because some groups will be less likely to respond to a voluntary survey.

The newly released documents back up a claim Sheikh made to the Commons committee last month that he quit his job over reports the agency recommended scrapping the mandatory census. Sheikh said those reports, which were based on statements by Clement, were damaging to the agency's credibility.

"The one and only factor that led to my decision that I made, was Statistics Canada's reputation," he said. "I thought that if I did not leave my job Statistics Canada's reputation would be tarnished for a long time to come -- and that was something I did not think that I could accept."

The Conservatives have said they plan to push ahead with a voluntary survey despite the controversy, arguing that the mandatory long-form census is too intrusive and a voluntary survey will produce sufficient data.

But opposition parties have described the move to a voluntary survey as a political manoeuvre designed to appeal to the Tories' electoral base.

With files from The Canadian Press