This would see Australia move from the present fixed carbon price of $24.15 a tonne to the floating European price, at present about $6 a tonne, on July 1, 2014.

Opposition leader Tony Abbott in Sydney earlier this month with Coalition environment spokesman Greg Hunt. The Coalition has attacked the government's move to an emissions trading scheme earlier than planned. Credit:Edwina Pickles

Treasurer Chris Bowen conceded on Monday that while the move would ease cost of living pressures, it would see a ''significant'' hit to the federal budget, in the billions of dollars.

But he would not be drawn on how much the carbon tax decision would cost the budget or what the government would do to pay for it - saying this would be announced in coming days. Mr Bowen also would not say whether or not Parliament would be recalled to legislate the changes before the federal election. He said the timing was up to the Prime Minister.

''One way or another'' - either through the Parliament or an election - Labor would seek a mandate to make the change, he told Fairfax Radio.