The Australian Workers' Union is to explore a strategic alliance with other unions operating in the agriculture supply chain in a bid to "grow union density" in the sector and campaign for employees rights.
AWU national secretary, Daniel Walton, said workers in the farm sector were routinely underpaid and denied basic working conditions.
The union, once led by Opposition leader Bill Shorten until he moved into federal politics, represents workers in farming, civil construction, mining and oil industry jobs.
The agriculture sector is rife with unscrupulous employers who exploit and abuse their workers
It is Australia's oldest union and its predecessor, the shearers union, is credited with effectively giving birth to the Australian Labor Party in western Queensland during an 1891 shearers' and pastoral workers' strike.
However, AWU membership has slumped in recent years, reportedly halving to about 69,800 last year - down from a strength of 139,329 declared in 2012.
It is now about half the size of the feisty Construction Forestry Maritime Mining and Energy Union, which shares some similar membership territory as the AWU.
"There are fewer areas tougher to organise than Australian agriculture," Mr Walton said.
"As a result, the sector is rife with unscrupulous employers who exploit and abuse their workers.
"These workers need a strong union presence.
However he said farm sector employees and their union needed "scale and muscle right along the supply chain".
This week's AWU conference has voted to assess alliance opportunities.
Discussions have already begun with the Transport Workers Union and the Shop Distributive and Allied Employees Association about a potential agriculture alliance.
"These unions have the strength and coverage to really make an impact," Mr Walton said.
"It is only logical that we look to pursue a similar alliance in agriculture.
AWU members and potential members, who harvested crops and packed them, needed to be in alliance with the workers who moved farm products across the country, and workers who put them on the shelves.
"The AWU was born in the bush and we won't turn our back on those who work there," he said, noting other union alliances had achieve similar goals.
"The Western Mine Workers' Alliance with the Construction Forestry Maritime Mining And Energy Union is a success.
"More recently, the Offshore Oil and Gas Alliance with the Maritime Union of Australia has delivered some of the fastest membership growth we have seen in modern times."
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