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The Mowat Centre, based at the University of Toronto, bills itself as a non-partisan think-tank. But multiple studies from across the political spectrum have found that in some provinces, existing tax structures mean no families will benefit. In others, some in high-income brackets would see only minimal financial savings.

Despite the criticism, however, the federal government has insisted it will press ahead with the measure.

The provinces would likely be on the hook because of the tax collection agreements all of them save Quebec have signed with the federal government over the last 50 years, the report said.

The deals mean there is only one tax collector for the various federal and provincial levies, which saves everyone money. But as a result, the affected provinces all use the same definition of taxable income.

That means if the federal government changes the definition, the provinces will have to go along.

The tax agreements are a key part of the economic union in Canada, Johal said.

“But at a certain point, if things like this keep happening and the cumulative impact of these decisions reaches a certain dollar value, the provinces are going to have to make an assessment: ’Is it really worth it to us to stay in these agreements if the federal government is going to continually make unilateral decisions?”’

But amendments to the agreements or an offer by the federal government to compensate the provinces for lost tax revenues are options that could be explored before the provinces just walk away, he added.

For example, Ontario’s agreement with Ottawa on the collection of the harmonized sales tax protects the province from any decision that would result in a 1% revenue decrease. If the province doesn’t agree with the decision in writing, the federal government has to pay up.