Opposition Leader Tony Abbott says his paid parental leave scheme will deliver "workplace justice" for new mums at a cost of $5.5 billion a year, offset by a business levy and budget savings.
Under the plan, working women will get 26 weeks' leave on full pay - up to a cap of $75,000 - plus superannuation for each baby born from July 1, 2015.
"This isn't a generous scheme, this is a fair scheme," Mr Abbott said on Sunday.
"It is an important question of workplace justice."
It will be funded in part by a 1.5 per cent levy on about 3000 companies earning more than $5 million in taxable income a year, which will be offset by a 1.5 per cent corporate tax cut from mid-2015.
The coalition estimates the net cost at $6 billion over the forward estimates, after budget savings and the scrapping of Labor's scheme.
Mr Abbott insists the tax cut, along with the fact that companies won't have to bear the cost of in-house maternity schemes, means the overall business burden won't rise.
"This scheme has been fully costed by the Parliamentary Budget Office and it is fully funded both by the levy on big business and by offsetting savings," he told Network Ten on Sunday.
The budget office is yet to release its full costing on the scheme, which will be Mr Abbott's "signature" policy if the coalition wins the September 7 election.
Payments would be made directly to new mothers by the Family Assistance Office, not their employer, whether they are in full time, part time or casual work.
Prime Minister Kevin Rudd says he doesn't understand the need to move away from the current "equitable" arrangements offering working women 18 weeks' pay at the minimum wage, particularly when the coalition is going to dump the schoolkids bonus for parents.
"I don't get it," he told reporters in Adelaide.
Labor also questions whether big business will support the levy.
Health Minister Tanya Plibersek says the coalition scheme offers more to women on high salaries than those on average or low salaries.
"It's incredibly unfair," she told Sky News.
"We don't give more to the people who already have more. We give more help to the people who need more help."
Labor's scheme doesn't include super.
Finance Minister Penny Wong says Mr Abbott's "expensive" plan will require budget cuts to pay for it.
Mr Abbott insists it's fully funded and costed and "doesn't make the fiscal situation worse".
He admits that 10 years ago he would have shunned such a policy.
"But if we want families to have more kids, if we want women to have a fair dinkum choice to have a family, and maybe to extend the size of their family and to have a career, we need a policy like this," he said.
Deputy Greens leader Adam Bandt says the Greens will back the scheme, but says it should be restricted to women earning less than $100,000 a year.
"We would seek to make it fairer and to start it sooner," he told reporters in Melbourne.
Mr Bandt says the starting date suggested the opposition is not completely committed to its plan.
"You wonder whether pushing it out further is a sign it might not happen at all," he said.
ACTU President Ged Kearney said the coalition should work to build on the current paid parental leave regime, rather than scrapping it and starting again.