The two Australian shipping ensigns, modified and approved by the British Admiralty, were gazetted in 1903. Source: Ralph Kelly, Flags Australia.:
Celebrations surrounding the inauguration of the new Commonwealth of Australia on 1 January in Sydney and at the opening of its first Federal Parliament on 9 May in Melbourne overshadowed Anniversary Day in 1901. Federation had been a remarkable political achievement. Colonies had jostled to protect their interests: New South Wales rivalling Victoria; and the smaller states fearing the larger states' combined political power. Led by the ANA in Victoria and the Australasian Federation League in New South Wales, the colonies chose to be self-governing within the British Empire, not independent outside it. They were Australian, but they were also British. As Parkes had reminded colonial representatives in Melbourne in 1890, 'The crimson thread of kinship runs through us all'.18 They belonged together because they shared not only a continent but also a British background. As a small white population of almost four million in a large continent far from Britain, Australians depended on the Royal Navy.
New Zealand and Fiji had both been invited to join the Australian Federation but had declined. The originally proposed name had been the Australasian Federation. But those damn kiwis were party poopers.
The story I read was that most Australian colonies and territories were assembled, apart from Western Australia and New Zealand. Cables from both were received, the Western Australian representatives were due to arrive in a few hours, but the New Zealand premier, Richard John Seddon, historically known in NZ as King Dick, informed the Australians that the NZ Government had declined to join the new Australian Federation, later to be known as the Australian Commonwealth. I wasn't aware that Fiji had been invited as well. New Zealand became a Dominion in 1901. Another story claimed an empty chair is kept for New Zealand at Commonwealth meetings in case NZ decides to change its mind and become part of the federation. Fact or just a good story? I wonder.