The Liberal Democrats have promised to kick off 2016 with a "big battle" over the Government's cuts to universal credit.
Leader Tim Farron has called on Labour and Tory rebels to support an amendment in the Lords that would block the changes before they come into force in April.
The Lib Dems say working families stand to lose more than £1,000 a year, arguing that the package would have an "almost identical" impact to the tax credit reforms abandoned by George Osborne earlier this month after a challenge in the Upper House.
Mr Farron said: "The first big political battle of 2016 is already looming. The Liberal Democrats worked hard to stop tax credit cuts and we won't let the Government bring it in through the back door.
"The Prime Minister and Chancellor claim they want to make work pay, but cuts to universal credit will mean people pocket less of what they earn.
"Their actions show they simply do not care about working people on low incomes.
"The big question is, after bottling voting in the Lords to stop tax credits this year, will Labour finally put their money where their mouth is and support Lib Dems when we attempt to put a stop to this attack on working people?"
The Lib Dems are expected to table an amendment to the Welfare Reform and Work Bill that would repeal the changes after the legislation completes its committee stage.