Labor has seized on the news, claiming it represents a "giant raid" on investors, while continuing to argue that the Coalition is hiding future cuts from voters.

The Coalition has already announced it will impose a 1.5 per cent levy on 3200 companies to help fund its $5.5 billion a year parental leave scheme, which would give women six months leave at their current salary, capped at $75,000. But it is yet to reveal the exact details of how it would be funded.

On Wednesday, Mr Abbott confirmed that the levy will not qualify for franking credits, meaning that shareholders would lose tax breaks on their dividends.

"Levies don't attract franking credits, that's just a standard rule," Mr Abbott told reporters in Brisbane.

In Australia, when companies pay their shareholders dividends they also give them a so-called "franking credit" for the tax they have paid creating those dividends. The shareholder can use it to cut their own tax. The more tax the company pays the less their shareholders pay.

Before Mr Abbott made the admission, Treasurer Chris Bowen said the Coalition's decision not to provide franking credits - reported to raise $1.6 billion for the parental leave scheme - meant the levy would be paid by every single shareholder in Australia.

"This is Tony Abbott's giant raid on Australian investors to pay for his unravelling signature policy," he told reporters in Melbourne.

"Why should a retiree who has been saving and working all their life pay for Tony Abbott's paid parental leave scheme through a tax on their savings?"

Mr Abbott has previously said that the Coalition "will make no unexpected, adverse changes to superannuation in our first term".

"Guess what, this is adverse and it is unexpected," Mr Bowen said.

Prime Minister Kevin Rudd also continued to pressure the Coalition to reveal detailed costings, which Mr Abbott has said will not be released until the final week of the election campaign.

"Mr Abbott is frightened that if the details came out on where the cuts would fall, what health services will be slashed and what schools will be defunded, that people will be frightened to vote for him," he said in Brisbane.

Mr Abbott defended the move, saying dividends would be higher for investors under a Coalition government "because the economy will be stronger".

Shadow treasurer Joe Hockey was also unapologetic, saying that the franking credits debate had been around since 2010. "This is not a new story, this is not a gotcha moment," he said.

"If Kevin Rudd wants a debate about the prosperity for self-funded retirees, bring it on."

Corporate Tax Association spokesman Frank Drenth has raised concerns about the franking credits issue.

"I really think the Coalition should think twice before compromising the dividend imputation system," he said. "It's not a well thought out policy."

When asked about the franking credits during an earlier media conference in Brisbane on Wednesday, Mr Abbott hailed his parental leave scheme as a "watershed" social advance for Australian women.

"Every social advance attracts its critics; every social advance since the beginning of time has attracted critics who said the world as we know it will end - if you pay people the pensions, if you introduce support for people with disabilities."

Queensland Premier Campbell Newman, standing alongside Mr Abbott at a sporting announcement, said state public servants would have the choice of opting in to the federal Coalition scheme.

Mr Newman said Mr Abbott's scheme was more generous than existing state parental leave schemes. The Queensland government would contribute funds to the federal government equivalent to the portion the state would have paid originally.

"I am 100 per cent behind this scheme," he said.

With Peter Martin, Daniel Hurst, AAP