The government's proposed £26,000 cap on benefits, one of the coalition's most divisive policies since coming to power, is facing a challenge from Liberal Democrats and Bishops in the Lords.
The bill will mean no family can claim more than £500-a-week in welfare, the equivalent amount of a £35,000 salary after tax.
As ministers face a showdown at the House of Lords, we take a look at who is for and against, and why.
FOR: Iain Duncan Smith, and the government. The work and pensions secretary insists the changes won't push families into poverty - and his policy is supported by 76% of the public according to YouGov polling.
IDS was backed up by the prime minister's official spokesperson who said on Monday "The key incentive we are trying to change is the incentive around work.
"We can't have a system where people are claiming benefits which are greater than you would get if you were in a job paying £35,000."
SITTING ON THE FENCE: Labour have taken a mixed position saying they support the camp in principle but are concerned about how it is being implemented. Shadow work and pensions secretary Liam Byrne has said Labour will support the bishops' amendment to exclude child benefit from the cap if the party's own amendment is defeated.
AGAINST: So why is it so controversial? In a blog for the Huffington Post CentreForum's chief economist Tim Leunig explains how an average family would have "only £1.64 to live on" under the cap.
"No alternative figures will make any difference: this is simply not a living income for a family with four children in private rented accommodation in a cheap part of outer London."
The Bishop of Ripon and Leeds, Rev John Packer, is attempting to change the bill to mean child benefit is excluded. He is supported by the child poverty action group, who argue that the policy is "based on a foundation of myths" and could push 210,000 children into "severe poverty and homelessness.
Chief Executive Alison Garnham added the Bishops' changes were sensible. "We hope a government that promised to be the most family friendly ever will prove it today by following their lead."
Take a look at our slideshow for a run-down of who's for and who's against the cap.
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