Labour has claimed the benefit changes in the Autumn Statement would leave the dole bill £6 billion higher.
Shadow work and pensions secretary Liam Byrne said Chancellor George Osborne's announcements last week slashed tax credits and maternity pay and would drive people out of work.
Mr Byrne took aim at the planned benefits uprating Bill, announced in the Autumn Statement last Wednesday, which will limit many working age benefits to an increase of 1% - below inflation and a real terms cut.
But the claims were rejected outright by Secretary of State Iain Duncan Smith in testy Commons exchanges during Department for Work and Pensions questions.
Mr Byrne said: "The Office for Budget Responsibility (OBR) says the dole bill will rise by £6 billion as a result of your failure to get Britain back to work.
"To pay that price, you're proposing an uprating Bill which I'm afraid to say sounds all wrong to me. It's wrong to take £4 billion from tax credits, it's wrong to take £300 million from maternity pay and it's wrong this strivers tax is going to hit 4,500 working families in your own constituency.
"You should be fixing welfare reform, not flogging working families. Perhaps you would like to tell us just what share of the savings from this uprating Bill is going to come from working families?"
Mr Duncan Smith said: "The reality is that even in all the forecasts our unemployment figures are better than the forecasts that were originally made by the OBR.
"Can I remind you that you left this Government with a 6% fall in GDP, an economy on the rack, debt that was higher than any other country in western Europe, debt rising every year, £120 million being spent to pay off that interest.
"Let me remind you of one other thing: every single debt change we have made, every cut, every change you have voted against. Labour are irresponsible and not fit for government."