The high-profile head of Australia's biggest manufacturing union has warned it will withdraw support for the Federal Government's carbon tax if "a single job" is lost under the scheme.

Australian Workers Union national secretary Paul Howes has warned the Government that "if one job is gone, our support [for the carbon tax] is gone".

Mr Howes has called a crisis meeting of AWU officials this morning to discuss the impact of the tax and the compensation package being offered to protect jobs.

He says he will not be making any more comments until after this morning's meeting.

Opposition Leader Tony Abbott seized on the union's concerns when speaking on Channel Nine this morning.

"They're very understandably taking the view that you can't compensate someone who's lost his or her job. If you've lost your job, where's the compensation?" he said.

Opposition Climate Change spokesman Greg Hunt says Prime Minister Julia Gillard will find it hard to guarantee no jobs will be lost.

"Today, the Prime Minister must make the guarantee that Paul Howes demanded, that not one job will be lost because of the carbon tax, to India, to China or to Indonesia," he said.

"But she can't make that guarantee because that's the reality."

Ms Gillard says she understands the union's position.

"Of course they want to make sure that their jobs are safe and I understand that," she said.

"I want to make sure that people have got jobs too which is why we're working with Australian businesses to design this scheme right and to get the assistance that helps industry transition and make the change right."

Federal Treasurer Wayne Swan has moved to reassure unions the Government is concerned about job losses.

Mr Swan says the Government's number one objective is to support jobs and future prosperity.

"Nothing could be more important to jobs in Australia and the future than making that transition," he said.

"We have to go to lower carbon emissions, there's no choice. We have to make the transition to a lower carbon emissions economy.

"That's what the Government is having a discussion with the business community about, and of course with unions and the wider community."

Dave Oliver from the Australian Manufacturing Workers Union (AMWU) is also worried about job losses, but has stopped short of saying the union would pull its support for the carbon tax.

Mr Oliver says the Government will need to provide assistance to protect existing jobs and provide incentives to attract investment in new jobs.

He says the AMWU understands there will be a period of transition when jobs will be in flux.

"We are concerned about the impact that pricing carbon will have on existing industries but we don't see it as an either/or proposition. We are taking a total look at it from net jobs - that there will be a transitional period, there will be some jobs that may go and transform into new jobs," he said.

"If we can get it right then our main focus is certainly in the area of opportunities for new employment in the clean technology sector."

Mr Oliver says he has been getting good feedback from AMWU members about reducing carbon.

"Our members get it. They understand we need to tackle climate change because the thing that has been lost in this whole debate is the environment and people understand that something needs to be done," he said.

"If the Government gets it right, has the scheme in place to attract the investment, it can create the jobs for the future."

Climate Change Minister Greg Combet says he is continuing to work with the unions and is consulting the affected industries.

"I understand there's a lot of concern and confusion about this issue. It is an important reform and it merits a lot of debate," he said.

The Australian Council of Trade Unions' Jeff Lawrence says the wider union movement supports putting a price on carbon.

"We absolutely are determined to make sure jobs are protected," he said.

"There's no division amongst unions, people are concerned but I think if we work through the process then those concerns will be addressed."