Australia can't afford PM's PPL: NAB boss

The outgoing boss of National Australia Bank has lashed Prime Minister Tony Abbott's planned paid parental leave scheme, saying the country cannot afford it.

Cameron Clyne, who stepped down as the bank's chief executive on Thursday, says the scheme would cost NAB $100 million and would not improve the participation of women in the workforce.

The $5.5 billion scheme that will pay up to $50,000 over six months for women having a baby will be paid for by a 1.5 per cent levy on more than 3000 of Australia's top companies, including the big four banks.

Mr Clyne said feedback he received from the bank's workforce indicated the biggest barrier to women re-entering the workforce was child care.

"If I could spend that $100 million on child care as opposed to a paid parental leave scheme, that would be far more productive," he told Fairfax radio.

Earlier, the prime minister said he remained committed to the scheme.

"I don't break promises and this was a promise I took to two elections," Mr Abbott said.