Tory leader David Cameron has come out against certain key sections of the welfare reform bill aimed at forcing single parents into work.
Speaking at his monthly press conference, Mr Cameron said forcing single parents of children aged only one-years-old into work was a "shameful proposal".
He continued: "We need to help families, not make life harder for them.
"It won't do much good for our economy and certainly won't do much good for our society."
Mr Cameron said he had no objection to the proposals being implemented once the children had fully entered primary school, but warned implementing it at a younger age threatened to negatively affect families.
"Many parents choose to go back to work and we should support them in that choice," he said.
"But the state prodding, pushing and cajoling you into work like this with children so young, I believe, is wrong."
He pledged to work with other MPs in the Commons - possibly including left-wing Labour rebels - to fight the proposals.
Liberal Democrat work and pensions spokesperson Jenny Willott said: "Why has it taken David Cameron so long to see sense on these proposals? The Liberal Democrats said last week that the attacks on single parents were unwarranted and had gone too far.
"It is clear public opinion is against persecuting single parents, yet it has taken the Conservatives a week to fall in step with popular sentiment."
Mr Cameron also argued there was now considerable difference between the Tories and Labour.
But the parties are united on the broad character of the wefare package, with Mr Cameron claiming his party all-but-wrote many of the policies.