Business leaders are urging Opposition Leader Bill Shorten to state his position on the Adani coal mine, amid conflicting statements by Labor candidates in marginal seats in Queensland and Melbourne.

The Labor leader has declined to explicitly rule out reviewing the project's federal environmental approvals if he becomes prime minister, noting only that he has "no plans". On Tuesday he revealed he would not sign a petition by the Construction, Forestry, Maritime, Mining and Energy Union outlining support for coal jobs.

Adani steps up pressure on Queensland government to approve mine.

Mr Shorten said he would not be bullied by unions or the environmentalists and would "adhere to the science, the law".

Australian Mines and Metals Association chief executive Steve Knott said jobseekers, businesses and regional communities "deserve certainty" about Labor's stance.

"It's not that hard for a political leader to say whether they support a project or not, given they've had the best part of a decade to consider it," Mr Knott said.

Labor's Dawson candidate, Belinda Hassan, added fuel to the fire while campaigning with Mr Shorten in the seat on Tuesday, saying a future Labor government may review the Adani mine's federal environmental approval.

Bill Shorten has refused to rule out reviewing the Adani mine's approval. Lukas Coch

While other Labor candidates in Queensland mining seats have expressed their support for the Adani project – calling for the Galilee Basin to be opened up to create thousands of jobs – that is not the case for those targeting Melbourne seats.

Josh Burns, Labor's pick to replace Michael Danby in the marginal seat of Macnamara, told a candidate forum earlier this month he opposed Adani.

"I don't want to see this thing built, and I don't want to see any other mine in the Galilee Basin being built – not Clive Palmer's and not Gina Rinehart's, and not some of the other mines that are waiting," Mr Burns said to applause from the inner-Melbourne crowd.

"I know that there is a lot of pressure on the Labor Party on this, and I hear you and I am absolutely with you on this issue," Mr Burns said. "I don't want to see this mine go ahead."

Zac Beers, the Labor candidate for Flynn, in Queensland, has signed the CFMMEU pledge, as has the party's candidate for Capricornia, coal miner Russell Robertson.

Mr Robertson told The Sydney Morning Herald and The Age: "I'm going to do my best to make sure every one of those six projects get up and running."

The union has threatened to campaign against Labor in Queensland coal seats if candidates do not sign its pledge.

In Townsville, the Labor member for Herbert, Cathy O'Toole, said she had not seen the CFMMEU pledge, which the union first demanded all federal election candidates sign in February.

However, she has signed a pledge drafted by the Queensland business community declaring support for "the immediate opening of the Galilee Basin and jobs for North Queensland".

Asked if she was frustrated by Mr Shorten's refusal to rule out a review of the Adani project's federal approval, Ms O'Toole said she had been "too focused on doing my job here lately" and that she would work to ensure that Townsville voters get their "fair share".

Townsville Enterprise chairman Kevin Gill said coal mining in the Galilee Basin would create "desperately needed jobs for North Queensland families", and called on all federal candidates to "stand with us". He vowed to publish a list showing "who stands with us and who doesn't" on Friday.

Mr Knott said Adani was pursuing a smaller, self-funded version of its original mine proposal, and that the project would "open up the enormous development potential of the Galilee Basin".

"We don't think it's unreasonable for the federal ALP to clearly state their position on the Adani project," he said.

"The industry also needs confidence that an ALP government would support new investment projects, not pander to noisy minority groups located thousands of kilometres away."