The filling of casual Senate vacancies was crucial to the constitutional crisis of 1975.
Without the breaking of the convention surrounding casual vacancies, the blocking of Supply by the Senate would not have been possible.
The convention was straight-forward: In the event of a senator’s death or resignation, the Constitution requires that a replacement be appointed by the Parliament of the State represented by the senator. In practice, the convention was to appoint a replacement from the same party, so as to maintain the balance of numbers in the Senate.
Following the elections of 1974, the composition of the Senate was:
- Liberal/Country Party: 30
- Australian Labor Party: 29
- Independent:1 (usually voted with the ALP)
On these figures, the Senate could not block the Budget, or other money bills, because the vote would be tied, and therefore defeated.
In January 1975, the Government appointed the Attorney-General, Senator Lionel Murphy, to the High Court, creating a Senate vacancy in New South Wales.
In June 1975, an ALP senator from Queensland, Bert Milliner, died, creating a Senate vacancy in that State.
Because the Section 15 of the Constitution requires State Parliaments to appoint replacements for Senate vacancies, without having a full statewide by-election, it had always been a convention that a member of the same party as the dead or resigned senator was appointed to fill the vacancy.
In the cases of Murphy and Milliner, however, the Liberal/Country Party government in NSW, led by Tom Lewis, and the Country/Liberal Party government in Queensland, led by Joh Bjelke-Petersen, chose to appoint non-Labor replacements. The numbers in the Senate thus became:
- Liberal/Country Party: 30
- Australian Labor Party: 27
- Independents: 3 (only one voting with the ALP)
This effectively gave control to the opposition parties. They did not have sufficient votes to pass their own motions, but they did have the requisite numbers to block the budget bills in October 1975.
In 1977, a constitutional amendment proposed by the Fraser government was carried at a referendum which now requires that Senate vacancies be filled by members from the same party or political group as the departed senator.
