Section 51(xxxi) of the Constitution of Australia requires 'just terms' (financial compensation) for property that is compulsorily acquired, so the federal government introduced the "Medicare Levy Amendment Act 1996" to raise the predicted cost of A$500 million through a one-off increase in the Medicare levy. The 'gun buy back scheme' started on 1 October 1996 and concluded on 30 September 1997. The Australian National Audit Office reported that the scheme compulsorily acquired more than 640,000 firearms, many of which were semi-automatic rifles and shotguns (restricted as a result of the 1996 legislative changes) or old, antique and dysfunctional firearms.