The constitutional text denies the Senate the power to originate or amend appropriation bills, in deference to the conventions of the classical Westminster system. Under a traditional Westminster system, the executive government is responsible for its use of public funds to the lower house, which has the power to bring down a government by blocking its access to supply – i.e. revenue appropriated through taxation. The arrangement as expressed in the Australian Constitution, however, still leaves the Senate with the power to reject supply bills or defer their passage – undoubtedly one of the Senate's most contentious and powerful abilities.
The ability to block supply was the origin of the 1975 Australian constitutional crisis. The Opposition used its numbers in the Senate to defer supply bills, refusing to deal with them until an election was called for both Houses of Parliament, an election which it hoped to win. The Prime Minister of the day, Gough Whitlam, contested the legitimacy of the blocking and refused to resign. The crisis brought to a head two Westminster conventions that, under the Australian constitutional system, were in conflict – firstly, that a government may continue to govern for as long as it has the support of the lower house, and secondly, that a government that no longer has access to supply must either resign or be dismissed. The crisis was resolved in November 1975 when Governor-General Sir John Kerr dismissed Whitlam's government and appointed a caretaker government on condition that elections for both houses of parliament be held. This action in itself was a source of controversy and debate continues on the proper usage of the Senate's ability to block supply and on whether such a power should even exist.
