Resources Minister, Josh Frydenberg, described Mr Shorten as a "risk to jobs and investment everywhere".

After weeks of being under siege, the Government saw a political opening, and jumped on Mr Shorten's comment yesterday that he opposes Adani's $16 billion coal mine project in Queensland.

It's accused the Opposition Leader of walking away from his previous support, purely and simply, because of the tight battle with the Greens in the Batman by-election.

"The only thing that has changed is the Batman by-election," Mr Frydenberg said.

"Bill Shorten is putting votes in Melbourne ahead of jobs in Queensland."

He had, he said, "appalled his own colleagues" after reports Labor frontbenchers had expressed anger at their leader's comments, and that he was "off the reservation".

"He's looking over his shoulder at other (leadership) contenders and now is at war with his own party.

"He can't be trusted with other projects.

"He's putting political opportunism ahead of science and the law."

Mr Shorten has previously said the massive project must stack up economically and environmentally. His office today repeated that Labor would not expose taxpayers to sovereign risks by tearing up contracts.

Mr Shorten later said he was “increasingly sceptical” about the project, and is yet to be convinced it “stacks up commercially or environmentally.”

But a Labor Government would not expose taxpayers to any future compensation claim by revoking licences.

“I’m not a fan of it,” he said.

“If approvals have been given, they stay,” Mr Shorten said.

“You can’t undo the past.”

Mr Shorten said no bank or super fund wanted to invest in the project, raising doubt it would ever go ahead.

He refused to comment on criticisms from unnamed Labor MPs.

Voters in Batman go to polls on Saturday March 17.