As a backbencher, McCay opposed amendments to the "Defence Act 1903" proposed by Billy Hughes of the Australian Labor Party that called for peacetime conscription. He accepted its necessity in wartime, but only for service within Australia. McCay believed that volunteers would always be plentiful, and he feared that peacetime conscription would result in militarism. He was re-elected unopposed in the 1903 election, the first in which Victorian women were eligible to vote. In 1904, McCay moved an amendment to the "Conciliation and Arbitration Act 1904" to remove the clause that empowered the Commonwealth Court of Conciliation and Arbitration to give preference to trade unions. The debate became unexpectedly heated and resulted in the fall of Chris Watson's Labor government. The Free Trade Party's George Reid became Prime Minister and offered McCay the post of Minister for Defence.