The Federal Government's negotiations for a carbon tax are set to get an on-screen push from a celebrity-backed campaign to boost support for a price on carbon.

The advertisement, which begins on television tonight, is funded by a coalition of unions and green groups.

The ad features two of Australia's best known actors, Cate Blanchett and Michael Caton, and urges Australians to "Say Yes" to a tax on carbon.

"What if we say yes, to making big companies pay, when they pollute our skies? We'd be saying yes to less carbon pollution," Caton says in the ad.

"And finally, doing something about climate change," Blanchett adds.

Youth Climate Coalition national director Ellen Sandell says the ads are trying to focus on the positives of a carbon tax.

"The debate at the moment has been quite negative unfortunately and we really want to bring it out of the negativity and out of the nitty gritty of the politics and say that Australians really do support cutting pollution and a clean energy economy," she said.

World Wildlife Foundation Australia CEO Dermot O'Gorman says the campaign is aimed at building community support for a tax and encouraging alternative energy sources.

"It's about saying yes to investments in clean energy," he said.

"It's saying yes to creating jobs in green technologies. It's saying yes to clean air and better health for our kids."

The "Say Yes" campaign, which is being launched in Sydney today, comes as the second day of multi-party talks gets underway in Canberra.

Climate Change Minister Greg Combet says the talks have been constructive, although he says it would not be appropriate to comment on the content of the discussions.

He says there is still work to be done before a carbon price is decided on.

"This is a process of going through a lot of very detailed, complex policy issues and we've got lots of work to do over the weekend," he said.

"I don't anticipate an outcome over the weekend, of course I've indicated previously that we're hopeful of having this finalised by late June so that we can look towards making an announcement in early July."

The Business Council of Australia has been criticised for its suggestion of a starting price of $10 a tonne for carbon, much less than the $30 to $40 a tonne initially flagged by the Government.