Schools have had to shell out £3.8 million to cover the legal costs of converting to academies after a surge in councils passing on the bill.
A Schools Week investigation has revealed that more than half of councils now impose penalty fees on schools that convert.
The charge varies from a couple of hundred pounds to £40,000 per school.
Some councils still maintain they are obliged to pay conversion fees, especially when schools are forced to become academies.
But 69 of 120 councils responding to a freedom of information request by Schools Week confirmed they now charge schools for the legal costs of conversion, raking in £1.7 million last year alone.