A federal opposition plan to repeal the carbon tax if it wins government has been labelled immoral by a senior Labor minister, who says such a move cannot go ahead.
Climate Change Minister Greg Combet said plans by Opposition Leader Tony Abbott to scrap the scheme would leave a $20.7 billion hole in the forward estimates.
"He's given us no indication at all how he would achieve those savings," Mr Combet told reporters.
"He cannot and he will not be able to remove the carbon pricing regime."
During his budget-in-reply, Mr Abbott outlined $5 billion in savings to fund tax cuts and fortnightly pension and benefits increases tied to the carbon tax compensation for households promised by the government.
However, Mr Combet said the opposition leader's figures didn't add up.
He committed Labor to opposing Mr Abbott's plans should the party find itself in opposition after the September 14 federal election.
"(A carbon price mechanism) is the right public policy position for this country," he said.
"All nations at the moment are working on an agreement to be concluded by 2015 to reduce greenhouse gas emissions and take account of the scientific advice.
"With all of this policy that is working, that is environmentally effective, that's economically responsible and socially fair, and what's more is essential if we are to tackle climate change and protect the interests of future generations, Mr Abbott's position on abolishing these measures is completely immoral."