OTTAWA -- A Crown corporation's decision to publicly comment on an NDP-backed bill is raising questions about whether the Conservative government is using the public service for partisan aims -- again.

The Canadian Mortgage and Housing Corp. claims on its website that the New Democrats' proposal for a national housing strategy will cost "$5.5 billion per year in rental subsidies alone."

The CHMC did not explain on their website how they arrived at the number nor was it explained by Conservative MPs and their party who used it all day Wednesday in their attacks on the bill.

The sudden emergence of a dollar value from a non-partisan Crown corporation left New Democrats and observers scratching their heads.

Bill C-400 doesn't contain measures that come with a clear price tag -- as an Opposition bill, it can't call for any new spending.

Instead, it calls for all levels of government to sit down with the private and civil sector to draw up a plan to ensure all Canadians have access to housing, using a number of defined parameters.

"A number of times the government referred to a costing study on a New Democrat private members' bill supporting, at last, affordable housing for Canadians," Cullen said in the House of Commons on Wednesday.

"I ask the government to table this document, if it even in fact exists."

Treasury Board President Tony Clement responded that the number comes from Human Resources and Skills Development Canada, the federal department that oversees the CHMC.

He said he'd be happy to provide the information.

Late Wednesday night, a spokeswoman for the corporation said they were doing their due diligence.

"The preparation and review of cost estimates on proposed opposition bills is necessary so that the government can make informed decisions. This is not partisan activity," Kate Munroe said in an email.

She said the figure was derived by assessing what subsidies would be required in order to meet the bill's demands that housing costs don't compromise people's abilities to meet other basic needs.

"The bill does not specify who would provide funding for the implementation of the Act, or the duration and limit of funding that would be required," she said.

"This could expose the government to significant financial risk and could place additional financial pressure on provinces and territories through possible implications for health and social assistance programs."

The bill was introduced over a year ago but was up for a vote Wednesday night. The CMHC's backgrounder was posted as the Tories spent the day attacking the bill as being "a dangerous new NDP spending scheme."

The bill was defeated.

The federal Conservatives have long resisted calls for anything that resembles a national housing strategy, though committees in both the Commons and the Senate have recommended such an approach.

The Harper government says its contributions since 2008 to combat homelessness, to support low-income households and existing affordable housing programs, have amounted to billions of dollars.

But much of the funding is set to expire next year.

Advocacy group Canada Without Poverty noted the NDP bill contains nothing beyond a promise to make a plan.

"It does not call for a new social housing program," the group said in a statement.

"It is about the development of a national housing strategy in keeping with human rights law."

The Canadian Housing and Renewal Association said without seeing an analysis or calculation, it does not know how CHMC would have put a dollar value on a strategy.

But the group's director of policy and programs said what is clear is the need for one.

"As recently released main estimates show declining federal support for social and affordable housing, we think partners -- all orders of government and non-government actors -- need to come together more now than ever, just as this bill would enable," Dallas Anderson said.

Public servants -- including those at Crown corporations -- are supposed to be the non-partisan army supporting the activities of government.

The government's communications policy is also explicit about how far public servants can go in communications, noting they are expected "to provide information services in a non-partisan fashion consistent with the principles of parliamentary democracy and ministerial responsibility."

So the New Democrats questioned why the CMHC was suddenly wading into this debate.

"If the government wants to debate bills, fine. Come into the House, let's have a debate on a national housing strategy," said New Democrat MP Charlie Angus.

"But just as it was with Mr. Fantino, it's inappropriate for them to use government websites -- which are supposed to be non-partisan -- to launch partisan Conservative attacks. It's a misuse of taxpayers' resources."

Late last year, two highly partisan letters appeared on the Canadian International Development Agency's website, written by Julian Fantino, the minister responsible.

One was posted under the headline: "Dear NDP: CIDA Does Not Need Your Economic Advice."

The other contrasted Liberal policies with those of the Tories.

Both were removed after being deemed inappropriate by the Prime Minister's Office.

The Conservatives have long been accused of blurring the line between the work of political operatives and the public service, notably with their use of the "Harper government" as a branding slogan for departmental news releases.

A series of emails obtained under the access-to-information law by The Canadian Press revealed public servants felt use of the phrase breached the communications policy but were being forced to do it anyway.