Green’s Dictionary of Slang

(Aus.) a non-union wharf worker.

1937		Workers’ Weekly (Sydney) 21 May 4/2: Embittered by the activities of ‘snipers,’ or non-union workers, and the lack of any definite policy of the union to solve the pressing labor problem on the Waterfront, about 100 members of the Waterside Workers’ Federation yesterday smeared headlines across the capitalist press, by physically driving about 25 snipers off the wharves.
1943		Mercury (Hobart) 1 May 14/3: ‘Snipers’ - non-union wharf labourers - rushed the Customs House, Sydney, to register for the waterfront labour reserve.
1954		Sydney Morn. Herald 2 Sept. 2/9: ‘In 1938 and 1939, when the owners controlled labour we had only 4,000 members, but there were more than 2,000 ‘snipers’ (non-union casual workers) in the industry,’ Mr. Heal said.