Labour will force a Commons vote over its plan for the independent budget watchdog to scrutinise parties' tax and spending plans ahead of the next election.
Ed Miliband's party has been pushing for the Office for Budget Responsibility (OBR) to be given the power to scrutinise manifesto commitments from opposition parties.
It will challenge Chancellor George Osborne to accept the proposal in the Commons on Wednesday.
The head of the OBR, Robert Chote, backed calls for it to cost the main parties' manifestos when he gave evidence to the Treasury Select Committee in March.
But he warned that there were "significant practical issues" with the idea, and admitted that Mr Osborne was against introducing it for next year's general election.
Shadow chancellor Ed Balls said: "In tough times it's even more important that the policies of all the parties are properly costed and funded. People rightly want to know that the sums add up.
"That's why I want every spending and tax measure in Labour's manifesto to be independently audited by the Office for Budget Responsibility. And I believe the Tories and Lib Dems should be willing to subject their manifestos to independent scrutiny too.
"But to give the OBR the legal power to do this before the next election we need cross-party support for my proposal.
"This policy has already won the support of some Conservative and Lib Dem MPs. George Osborne used to say he was interested in this idea. But now that the election is approaching he seems to be resisting it.
"Robert Chote has said cross-party agreement would be needed by the early summer to do this for next year's manifestos.
"This week's debate is George Osborne's last chance to stop blocking this important reform. I hope he will change his mind and do the right thing."