The Liberals introduced a new bill Thursday to bring back the mandatory long-form census, which the Conservative government intends to replace with a volunteer option.

Liberal finance critic John McCallum said the bill is an attempt to undo the damage that will be done if the Conservatives go through with their plan. The move comes after months of sparring with the Conservatives over the controversial decision.

"Liberals believe that sound information helps make sound decisions," McCallum said in a release.

"That's why we will fix the mess Stephen Harper created by reinstating the mandatory long-form census and ensuring the threat of jail time is removed in the Act."

The Conservatives have argued that the census is invasive to Canadians and that the threat of jail time for those who refuse to comply, is heavy handed.

McCallum said the Liberal legislation, which will be tabled on Sept. 20 when Parliament resumes, will remove the threat of prison time.

The Bill specifies that 20 per cent of Canadians will receive a mandatory long-form questionnaire at census time. While jail time will not be a factor, Canadians would be legally required to complete it.

McCallum dismissed the Conservatives' concerns about privacy, saying that argument is a smoke screen hiding the party's true goal: hamstringing government's ability to deliver progressive social programs.

He called the census vital to Canada's interests, saying: "As one business person put it recently, the first rule of business is 'you can't manage what you can't measure.'"

The Conservatives and Prime Minister Stephen Harper have faced months of opposition to the decision, which was widely panned by academics and organizations, including Munir Sheikh, the former head of Statistics Canada, which relies heavily on the data from the long-form census.

One of the main criticisms of the Tories' move is that data collected under a new, voluntary system will not be comparable to decades of data already collected in past decades, rendering it virtually obsolete.

McCallum said the move would also provide an inaccurate picture of Canada, because lower income, minority groups would be less likely to participate in a voluntary survey.

Dimitri Soudas, Prime Minister Stephen Harper's director of communications, quickly shot back, telling The Globe and Mail that the statement shows Liberals' tendency to "constantly look down on working class people."

He said it is wrong to assume that minorities and the poor need to be threatened with jail time in order to participate in the census.

"We believe that freedom is an essential Canadian value, and we don't think that it is right to try to frighten or intimidate people into surrendering huge amounts of private information to the government," Soudas said.

Recently the Conservatives said they would add language questions to the short-form version of the census, which were previously only included on the long-form census.