German multinational Siemens has signed on to work for Adani's Queensland coal mine in spite of a warning from Australian Greens leader Richard Di Natale that it risked damaging its global reputation over a "dangerous project".

Key points: Senator Di Natale wrote to the head of Siemens urging him to ditch the Adani deal

Senator Di Natale wrote to the head of Siemens urging him to ditch the Adani deal Siemens has proceeded with the deal earlier than expected

Siemens has proceeded with the deal earlier than expected Resources Minister Matt Canavan is "not too worried" about the Greens leader's letter

Adani announced on Wednesday that Siemens had signed a deal to provide signalling for Adani's rail network to haul coal from the Carmichael mine.

Senator Di Natale wrote to Siemens boss Joe Kaeser in Munich on Tuesday, urging him to walk away from a "carbon bomb that the world cannot afford".

The Greens leader told Mr Kaeser in the letter that given Siemens' "great work on clean energy technologies" and its collaborations with Australian universities it was "crucial that Siemens' reputation stays in good health".

"There is a very real chance of reputational damage amongst the university sector, as well as across Australian and global operations generally as a result of Siemens profiting from the Adani mine," Senator Di Natale wrote.

"On behalf of millions of Australians, I urge you to not proceed with this contract and at least pause before signing on the 13th December, so that the board can properly consider the implications for Siemens, should this project proceed."

Richard Di Natale wrote to Siemens boss Joe Kaeser urging him to reject the Adani deal. ( ABC News: Matt Roberts )

Instead, Siemens has proceeded with the deal two days earlier than expected.

Senator Di Natale said in the letter that Australia's east coast was "inundated with mega fires of which we have never seen the likes before" and "our most populated city, Sydney [being] covered in smoke and ash for days with air quality 11 times above hazardous levels".

"This is all occurring at just one degree of warming. The International Energy Agency has said not one coal, oil or gas production facility can go ahead if we want to stay below 1.5 degrees (Celsius) of warming," Senator Di Natale wrote.

"In order to stay below 1.5 degrees of warming, or to have any hope of not exceeding 2 degrees, this massive coal mine simply cannot go ahead."

Stop Adani protests have targeted contractors involved with the project. ( AAP: Joel Carrett )

Senator Di Natale told the ABC Australians would be "appalled by this decision Siemens made".

"We are incredibly disappointed that Siemens looks like it has now signed a contract with Adani to support that mine when Siemens says they're committed to climate change action," he said.

Senator Di Natale said the company would remain under pressure to cut ties with Adani.

"It's clear the Liberal Party aren't going to do anything when it comes to stopping the polluting Adani coal mine, so we're focusing on those businesses that are facilitating the Adani coal mine."

Senator Di Natale said it appeared Adani had fast-tracked the contract after Siemens came under pressure from activists, including those who set up a protest camp outside Siemens' Melbourne office on Wednesday.

The ABC has seen documents leaked to activists by a number of Siemens staff to help with targeting the company.

Two industry insiders said Siemens was one of only three companies in Australia that could carry out the signalling work, but the other two had said no to Adani in 2017.

One of the insiders told the ABC at least one subcontractor had rejected an approach by Siemens to do the Adani work for "environmental" reasons.

Activists have vowed to maintain pressure on Siemens until it withdraws from the controversial project.

It is understood the work is worth $31 million to Siemens.

'Not too worried'

Matt Canavan says Adani is well-respected. ( ABC News: Lily Nothling )

Federal Resources Minister Matt Canavan dismissed the Greens leader's intervention as "this sort of provincial view, from a minor party leader from Victoria".

"I don't think Richard Di Natale is all that relevant an individual on these sort of issues," he said.

"I don't think people are going to listen to him so much. His views on it are well-known and good luck to him.

"The facts are that Adani's a well-respected company around the world — they just signed a big deal, a billion-dollar deal with Total, the French national gas company."

Mr Canavan said he was "not too worried" about Mr Di Natale's letter.

But he said "increasingly threatening tactics" from environmental groups justified the Morrison Government examining new laws to crack down on certain forms of protest.

Mr Canavan said he would leave it to scientists to determine whether or not climate change is contributing to elevated bushfire risk in Australia.

He said if there was a greater bushfire risk as a result of climate change, there should be "more tree clearing" to alleviate that risk, as well as "significant commitments to reduce carbon emissions by 2030".

A Stop Adani sign formed by people on Bondi Beach. ( Twitter: @stopadani )

'Siemens staff hate the idea'

Ben Pennings from the anti-mining group Galilee Blockade said Siemens was "making a billion-dollar gamble for a $31m contract".

"We're confident our ongoing pressure will convince Siemens in Germany to rein in the Australian operation so they can keep any semblance of being a responsible corporation," Mr Pennings said.

"Siemens staff hate the idea of working with Adani and we'll ensure that graduates choose more ethical companies.

"We expect staff will continue to leak information and Siemens can be assured we'll act on it so the Adani coal railway never proceeds."

Adani said in a statement the rail signalling project would create "up to 50 local jobs in Queensland including project staff, engineers and construction workers".

"We are pleased to be working with Siemens as the company is known for its exceptional experience in building rail signalling infrastructure around the world," Carmichael project director David Boshoff said.

An Adani spokeswoman declined to comment further.

Siemens has been contacted for comment.