Canada is being forced to shoulder a bigger share of the costs of developing F-35 fighter jets even though it has not decided whether it will actually buy any.

Canada is one of nine partner countries in the F-35 project, all of which are required to cover a portion of the stealth fighter's development costs to stay at the table.

Each country pays based on the number of F-35s it's expecting to buy, and Canada's pitched in more than half-a-billion dollars over the last 20 years, including $54 million last year.

But that amount was based on the Stephen Harper government's plan to buy 65 new fighter jets to replace Canada's aging CF-18s, which the Trudeau government has since officially increased to 88.

Even though Canada has not committed that those 88 jets will be F-35s, Defence Department officials say that change means it will have to pay more to remain a partner — including about $72 million this year.

The government has said it plans to keep Canada in the F-35 development effort until a replacement for the CF-18s is selected, which won't happen for two or three more years.

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