Generally, interest does not accrue on such unless the condo agreement or other such contract tacitly or explicitly refers to such. In this case, if there was no agreement, the condo corp would have to argue that interest on overdue fees was assumed, likely at the Court of Justice Act rate of 3%. However, you could certainly argue against it saying that interest was never part of the agreement and thus should not be applied, especially if they are requesting a high rate.
In summary, I don't see interest accruing if it was not previously agreed upon. However, if they litigate this matter, the judge may impute a reasonable interest rate if s/he feels just.
Hopefully that is of assistance.
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