Labour's interim leader Harriet Harman is facing a potential revolt by the party's MPs in today's Commons vote on the government's welfare bill.
Ms Harman has faced criticism from some Labour MPs after suggesting the party would not oppose some Tory cuts because voters do not want that.
She has backed moves to reduce the household welfare cap and restrict tax credit and universal credit payments to two children, arguing that there is a clear public appetite.
Warning that Labour's general election defeat showed it could no longer afford to oppose all such austerity measures, Ms Harman also announced MPs would not oppose the Welfare Reform and Work Bill.
But after a backlash from many MPs including leadership contenders Andy Burnham, Yvette Cooper and Jeremy Corbyn, she was forced to accept demands to table an amendment seeking to block it.
Writing in the Guardian, Chancellor George Osborne said Ms Harman's stance was a "step forward" in British politics.
"She recognised something else important in a democracy: that oppositions advance only when they stop blaming the public for their defeat and recognise that some of the arguments made by political opponents should be listened to", he added.
Mr Osborne also urged "moderate Labour MPs not to make the same mistake as in the last parliament, when they refused to support each and every welfare reform we proposed. I say: vote with us today."