The government eliminated the mandatory long questionnaire in late June, arguing it was intrusive and the threat of jail was overly coercive. (CBC)

The Conservative government admitted internally that switching to a voluntary survey from a mandatory long-form census would make some data unusable for federal institutions, documents submitted Monday in Federal Court show.

The admission lies at the heart of a court challenge against the government filed by a group that represents minority francophone communities across the country.

The Federation of Francophone and Acadian Communities argues that Ottawa will no longer be able to fulfil its obligations under the Official Languages Act without reliable data from the mandatory, long-form census. It wants the court to restore the long-form census quickly, saying government officials see the middle of next week as the deadline for any change.

The government eliminated the mandatory long questionnaire in late June, arguing it was intrusive and the threat of jail was overly coercive. In July, then chief statistician Munir Sheikh ordered the creation of a new, voluntary survey on behalf of Industry Minister Tony Clement.

The order, obtained by the federation for the court case, describes the resulting impact on the data collected by Statistics Canada.

"It is recognized that the quality of the data collected by the voluntary [survey] will be lower than that of a mandatory survey," the order reads.

It lists 39 federal institutions that use census data and goes on to warn that some information will simply be lost.

Some survey data, "will not be useable for a range of objectives for which the census information would be needed," wrote Rosemary Bander, the assistant chief statistician.

Other statisticians have noted that with lower response rates expected from a voluntary survey, producing neighbourhood and community data will no longer be possible.

Previously released Statistics Canada documents revealed the agency is not sure how much reliable data the survey will produce, or when it would be available for release.

Government duty to 'enhance' communities

The francophone federation's lawyer, Rupert Baudais, outlined to Federal Court Judge Richard Boivin the provisions of the Official Languages Act that require the government to proactively "enhance the vitality" of French and English minority communities.

The Conservative cabinet tried to respond to some of the federation's concerns by including more questions about official languages in the mandatory short census, but the group feels a simple counting of heads doesn't go far enough.

The long questionnaire contains detailed questions on points such as the level of education achieved, housing, and employment.

"The government must know what our needs are terms of health, of education, of everything, to know how to better deliver services and programs and respond to our needs," said federation president Marie-France Kenney.

"Our needs are very different from one end of the country to the next and often our communities are scattered and very small."

Sheikh resigned in July, unhappy with the suggestion by the Conservative government that he had recommended the survey as a suitable replacement for the mandatory long-form census.

Liberals to introduce Census bill

Meanwhile, the Liberals expect to have a private member's bill to write the long-form census into law introduced in the Commons by the end of the week. They also have an opposition day motion set for debate on Tuesday.

They expect that the NDP and Bloc Quebecois will support both the motion and the bill.

Liberal House Leader Ralph Goodale acknowledged it will be an uphill fight to get the bill through the Commons and then through the Senate, where the Tories are on the cusp of a clear majority.

"The damage is done by one nasty, brutish and short Conservative term in office . . . That messes up the ability to compare numbers going forward and to compare numbers going backward," Goodale told reporters Tuesday.

"It's not just a trivial little thing. That's why we're fighting it with everything we've got, because this is just fundamentally wrong."