Labor has sought to highlight the electorates where families with kids in childcare will be worse off under the government's new subsidy system.
The federal government has accused Labor of wanting to waste taxpayer money subsidising childcare for parents sitting around at home.
The opposition has sought to highlight the losers from the changes starting in July, using a new breakdown of which electorates contain the 279,000 families that will be worse off.
Early childhood spokeswoman Amanda Rishworth says data the opposition obtained under freedom of information show Labor-held electorates of Lalor, Rankin and Blaxland are the top three where families will lose out.
"The government for months has been trying to convince Australians that families will only be better off under their childcare changes," she told reporters on Sunday.
"What the figures reveal is that families right across Australia will be affected and indeed the majority of families who will be affected are in the two lowest income brackets."
However, the figures show that while the electorates Ms Rishworth highlighted are the biggest losers in terms of the number of families, it is Prime Minister Malcolm Turnbull's own seat of Wentworth where the highest proportion of subsidies will be lost.
Nearly half the families who now get childcare subsidies in the wealthy Sydney suburbs he represents will lose out from July.
More than two in five families in other blue-ribbon Liberal seats of Goldstein, Curtin, Warringah, North Sydney and Higgins will lose payments.
Education Minister Simon Birmingham says overall more than a million families will get higher subsidies for their children's care under the new system.
"This is about helping those families who are working the longest hours and earning the least amount of money," he told reporters.
Under the changes, which passed parliament last March, existing childcare subsidies will be rolled into a single payment.
Both parents must be working, looking for work, studying or volunteering for at least eight hours a fortnight to be eligible and families with a combined income of more than $350,000 won't get any subsidy.
"Is the Labor Party really saying they want more taxpayer dollars to support child care for people who are sitting at home?" the minister said.
"Because, frankly, that would be a waste of taxpayer dollars."
Parents can use an estimator on the federal education department's website to calculate how much subsidy they will be eligible for under the new system.