Windfall tax (Australia)

In Australia, windfall tax may refer to either:
In both cases, windfall tax originates in High Court decisions that certain state taxes were unconstitutional. Thus, the States were required to repay to the taxpayers the amounts previously collected under these unconstitutional taxes. The purpose of the windfall taxes were to treat these repayments as income to the taxpayer, and impose a Commonwealth tax upon that income at a rate of 100%. Thus, even though the tax laws in question had been declared unconstitutional, the taxpayers effectively did not receive any repayments; rather, the amounts due back to them from the States were taxed by the Commonwealth. The Commonwealth would then repay these amounts to the States, with the result that the States were not in any financial disadvantage.