Industry Canada has dampened expectations for the troubled project, now estimating Canadian companies are eligible to bid on as much as US$9.8 billion in contracts — down from US$12 billion.
Opposition New Democrats seized on the revision and noted that none of the figures are guaranteed.
A senior official told a parliamentary committee that almost 75 per cent of the revised figure is expected be gobbled up by the 70 companies that have already signed agreements with manufacturer Lockheed Martin.
The projection assumes the contracts are renewed throughout the nearly 50 years the fighter is expected to be in service.
New Democrat MP David Christopherson says the Conservative government will spend "ten of billions of dollars and hope that Canadian industry will benefit."
Government House Leader Peter Van Loan says Canadian companies have already signed more than $435 million in contracts and has committed to looking for ways to boost benefits and participation.
The Conservatives have cited the US$12 billion figure as part of the justification for not considering alternative aircraft.
Canada's auditor general has raised concerns about industrial benefits, saying there has been no clear, independent justification for the figure.
Michael Ferguson also said the air force has relied too heavily on data and assurances from the U.S. manufacturer, Lockheed Martin.
Christopherson said under traditional military procurements, the government could have demanded dollar-for-dollar regional benefits.
That means if the proposed contract was worth $25 billion as the auditor general suggests, the Canadian government could have asked for an equal amount in contract awards.
A small link in the government paper trail justifying the decision to purchase the F-35 was obtained by The Canadian Press late Friday.
A brief paragraph-long letter from National Defence to the department of Public Works outlines the air force's technical requirements in the barest of detail and states the F-35 is the only fighter that meets them.
The document also points out the fact many other countries are also purchasing the F-35, ensuring "long-term essential interoperability."
The auditor-general pointed to the letter as an example of how public works didn't conduct proper due diligence in signing off on the purchases.
NDP defence critic Jack Harris noted that the letter was requested of the Defence department and produced on the same day.
"There's nothing in the document to justify such an enormous purchase," he said late Friday.
What should have been given to public works was the military's full statement of requirements, which outlines in detail the kind of missions the jetfighter would have been expected to perform, among other things.
"The lack of due diligence is shocking. There's no other word for it."