Convention dictated that Federal Senate casual vacancies were filled by someone nominated by the same political party. However, on 27 February, the New South Wales Liberal Party Premier, Tom Lewis, defied the convention by appointing Bunton, who was not affiliated with any party. Facing a hostile Labor Party (and a sometimes hostile electorate), Bunton surprised many observers by acting independently rather than as a Liberal appointee, and resisted urgings from the Malcolm Fraser-led Opposition to block the supply bills of Prime Minister Gough Whitlam's government, instead supporting Labor on the supply bills during the 1975 Australian constitutional crisis.