Mine-workers union the CFMEU has come out strongly in support of Hunter MP Joel Fitzgibbon, despite Labor's pre-election commitment to shift towards renewable energy.
The Newcastle Herald has been told One Nation's candidate for Hunter, mine worker Stuart Bonds, has reached out to colleagues about drumming up support for his campaign.
But the Construction, Forestry, Maritime, Mining and Energy Union is urging its members not to vote for One Nation on May 18 due to the party's "anti-worker policies and record".
CFMEU northern mining and NSW energy district president Peter Jordan said on Monday that One Nation voted consistently against the interests of workers.
One Nation backs the bosses every time. They will never have our support.Peter Jordan, CFMEU
"This election there are many politicians cynically pretending to be the friend of coalminers. But they should be judged on their records, not their rhetoric," he said.
"One Nation has never supported workers. It has opposed penalty rates, supported the Australian Building and Construction Commission, opposed stronger protections for worker safety and opposed measures to boost apprenticeships.
"One Nation backs the bosses every time. They will never have our support."
Labor's energy policy includes a target of 50 per cent renewables by 2030, but Mr Jordan said the party offered the best policies to support permanent jobs.
"Labor has said consistently that coal will be an important part of Australia's energy mix going forward and that coal exports will continue for many decades."
The union has been less enthusiastic about Labor in Queensland, where the party's position on the proposed Adani mine is unclear.
The CFMEU Queensland mining division last week asked the state's Labor candidates to sign a pledge backing coal industry jobs.
Mr Jordan said the increasing use of casual labour in the mining industry was a key election issue in the Hunter.
"Under the Liberal National Coalition federally, we've seen casual work skyrocket," he said.
"At many Hunter Valley coalmines, half of all jobs are now casual at much lower rates of pay. This is a disgraceful record.
"Labor has committed to ending the 'permanent casual' labour-hire rort with commitments to same job, same pay for labour-hire workers and rights for casuals to convert to permanent work.
"This will reverse the rotten trend towards low-paid, casual work in our region."