The Constitution Alteration (Senate Casual Vacancies) Bill 1977, was a successful proposal to alter the Australian Constitution concerning the filling of casual vacancies in the Senate. It was put to voters for approval in a referendum held on 21 May 1977. After being approved in the referendum, it received the royal assent and became law on 29 July 1977. Prior to the amendment: the legislature of the relevant state was not required to have regard to the political allegiances of the replacement senator, and the new senator's term continued only until the next general election for either the House of Representatives or the Senate, or the end of the original senator's term, whichever happened earlier. The amendment changed this procedure by providing that: a state legislature replace a senator with a member of the same political party, and the new senator's term continue until the end of the original senator's term. Its intended purpose was to prevent major changes in the balance of power in the senate in the middle of a parliamentary term, but as it did not provide any time limit within which the appointment had to be made, the state legislature remained free to decline to fill the vacancy. As Section 11 of the Constitution permits the Senate to carry on despite the failure to fill any vacancy, the amendment did not completely solve the problem. On the same day as the vote on the casual vacancies amendment, four other questions were also put to the electorate. These concerned the: Simultaneous elections amendment Referendums amendment Retirement of judges amendment National song plebiscite. Overview The casual vacancies amendment came about as part of the political fallout from the Australian constitutional crisis of 1975. In the aftermath of this crisis, four amendments were recommended by sessions of the Australian Constitutional Convention, including one that would change the procedure for appointing replacement senators. All four were put to voters on 21 May 1977, and all were passed except the proposal for simultaneous elections to the House of Representatives and Senate. The casual vacancies proposal arose out of the 1975 controversy over the appointment of independent Cleaver Bunton (New South Wales) and anti-Whitlam Australian Labor Party member Albert Field (Queensland) to fill Senate seats formerly held by ALP senators. The appointments ran counter to a longstanding convention that when a Senate seat became open due to a casual vacancy, the state