Cuts to lone parents' payments are "straight out of Margaret Thatcher's book of policies," Fianna Fáil leader Michéal Martin told the Dáil.
Mr Martin urged the Government to reverse changes to the lone parent support scheme, another phase of which are due to take effect on July 1.
The FF leader described the changes as the "Burton cuts", as they are being implemented by Social Protection Minister and Labour leader Joan Burton.
Mr Martin said the changes were especially hard on single working mothers, citing the example of a mother working 20 hours a week, who will lose €108 per week.
Taoiseach Enda Kenny said 30,000 single mothers would benefit in the medium and longer-term from the changes.
He said 20,000 of these parents would have no change or actually gain, while the remaining 10,000 could increase the numbers of hours they work.
Mr Kenny said New Zealand and the Netherlands each end the payment when the child is five years old.