Treasurer Joe Hockey says the Government never promised not to introduce new taxes, pointing to the 1.5 per cent tax increase on big business that is proposed to fund the paid parental leave (PPL) scheme.

The Government is staring down backbench dissent over the idea, saying raising income taxes for the rich is the only the way the wealthy can contribute to repaying the debt.

But Liberal MPs, including Queensland backbencher Teresa Gambaro, say it is a breach of the Coalition's promise not to introduce any new taxes.

Mr Hockey has told the Australian Financial Review the belief that the Coalition never promised new taxes is "wrong".

"We went to the last election promising to introduce a levy for PPL so claims that we said we would never introduce new taxes are just wrong," he said.

"We actually went to the last election with a written policy saying we were introducing the 1.5 per cent levy for PPL."

Cabinet signed off on a debt levy yesterday with Finance Minister Mathias Cormann pleading with his colleagues and voters to trust the Government.

Meanwhile, former treasurer Wayne Swan says he left the budget in "sound shape".

Mr Hockey says if left unchecked there will be $123 billion of deficits and $667 billion of debt, based on last year's mid-year economic fiscal outlook.