Open this photo in gallery Parliamentary Budget Officer Yves Giroux pose for a portrait Nov. 14, 2018. Dave Chan/The Globe and Mail

The Conservative Party says it has concerns about an arrangement between the Parliamentary Budget Officer and the Finance Department that will see ministry officials pitching in to determine the cost of election promises in the run-up to the 2019 federal election.

The Tories’ finance critic, Pierre Poilievre, is questioning whether his party will participate, arguing that opposition parties that use the process would risk letting Liberal cabinet ministers and their political aides get an advance peek at their rivals’ campaign plans.

The decision to expand the PBO’s mandate to include assessing the cost of campaign promises was first proposed by the Liberals during the 2015 election campaign and was made law through an omnibus budget bill in 2017. The PBO released new details on Friday outlining how the process will work.

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The government approved the change over the objections of then-PBO Jean-Denis Fréchette, who expressed concerns that the office’s non-partisan staff would be placed in the awkward position of helping political parties craft their election platforms.

In an interview with The Globe and Mail, new PBO Yves Giroux said his career as a public servant makes him confident that departments can work on these sensitive files without tipping off the political actors they work with; he said the PBO will not tell public servants which political party has submitted the proposed campaign promise.

“My experience in the public service is public servants can keep a secret,” he said. “The leaks that I’ve seen in my career very rarely originated from the public service. I’m confident that it will be confidential. Public servants won’t talk to the ministers.”

Mr. Poilievre isn’t so sure.

“I can imagine every opposition party is going to have a problem with handing over key elements of a platform to a government department headed by a Liberal minister,” he said. “There’s a chance that a special quarantined unit over at Finance Canada could keep all of the platform secrets to itself, but it’s a chance. There’s also a chance that over a coffee at the Flaherty Building cafeteria, somebody mentions something under someone’s breath or that somebody in the minister’s office inadvertently finds out something about an opposition platform.”

(The Finance Department’s headquarters is named after the late Jim Flaherty, a former cabinet colleague of Mr. Poilievre.)

Conservative MP Ed Fast, who co-chairs his party’s campaign platform development team, confirmed the party has strong reservations about the PBO process and the connection to government departments led by Liberal ministers.

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A spokesperson for the Finance Department said the memorandum of understanding signed this month with the PBO places oversight of costing requests in the hands of the department’s non-partisan deputy minister. The spokesperson said no costing information will be shared with the minister or political staff.

NDP finance critic Peter Julian said he does not share Mr. Poilievre’s concerns.

“Even though I can’t say without question that there might not be some manipulations through the federal Finance Ministry, the reality is I think Canadians trust the PBO to provide an accurate evaluation of the respective campaign platforms,” he said. “That is important and that outweighs whether or not in some way or another the Finance Ministry is used in a partisan way.”

The 2017 changes to the PBO’s mandate also coincided with making the office a fully independent Officer of Parliament – rather than a division of the Library of Parliament – and giving it a bigger budget.

When the office was created in 2008 under a Conservative government as an independent source of financial information for MPs, its annual budget was about $2.6-million and the office had about 15 staff on average from 2008 to 2017. Now it has a budget of $7-million a year and a payroll for 41 full-time employees.

The detailed rules released Friday hint at the political challenges the spending watchdog could face. One says the PBO could refuse to determine the cost of a campaign promise if it believes “it is not a sincere policy objective of the party … and is instead being used to discredit the platform of another party.”

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Mr. Giroux, who has led the PBO since September, said reviewing promises will be challenging but his office is ready for the job.

“Whatever cost we come up with, somebody’s bound to be unhappy – either the party that requested it or other parties – and that may lead to accusations of partisan bias, so that’s the part of the electoral platform costing that makes me a bit uncomfortable,” he said. “I accepted the job knowing it was part of the mandate so I knew what I was getting into.”