Sousa writes that the transition funding, which Ottawa says was a temporary measure ending this year, should be included in Ottawa's budget, which is due out Tuesday.
Premier Kathleen Wynne has accused the Tories of balancing their books on the backs of Ontarians by cutting the amount of federal dollars returned to the province.
Federal officials have said the amounts are adjusted year-to-year based on a province's economic strength, and that Ontario's share in 2014 has changed because its economy improved relative to other "have-not" provinces.
But Sousa's letter says the province needs a "reliable and consistent" source of funding for projects such as the Ring of Fire.
"Ontario has always been, and continues to be, a net contributor to the federation. At a minimum, Ontario hopes to see the transition funding in your next budget to ensure fairness for Ontario families", Sousa's letter states.
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