Controversial plans to cut hundreds of pounds worth of tax credits from millions of UK families will go before the House of Lords later today.
Labour and the Liberal Democrats strongly oppose the cuts and a number of prominent Conservatives have also voiced concern.
Here's what you need to know:
- What are the proposals?
The Conservatives want to cut £4.4 billion from the country's welfare bill by reducing tax credits.
It will mean more than three million families losing an average of £1,300 a year from April.
- What are the arguments for and against?
For: Ministers say the drop in income will be balanced out by an increase in the minimum wage, as a new National Living Wage comes into force in February.
There will also be increase in the personal tax allowance and more free childcare from April next year.
Against: The Institute for Fiscal Studies claims that in reality, these changes will only make up for a fraction of the money lost. The Chancellor has also refused to publish a Treasury analysis to justify the figures.
Others have also argued that the people it will hurt most are those in work, but on low incomes - potentially damaging the Tories' aim to become the 'party for working people'.
- So what happens today?
The plans have already been voted through the House of Commons, and today the House of Lords will decide whether to pass, delay or reject the cuts.
- How much power does the House of Lords have?
According to century-old conventions, the Lords - an entirely unelected body - are not supposed to block financial measures approved by elected MPs or contained within manifesto commitments.
Senior political figures have warned of serious repercussions if they decide to ignore this policy on this vote, labelling the possibility "constitutional vandalism".
However, peers have argued that they are free to act in this case because these specific measures were not set out before the election in May, and are being pushed through as a Statutory Instrument instead of a formal Bill.
Baroness Angela Smith of Basildon, Labour's leader in the Lords, said this had been done to deliberately "sidestep the more usual detailed parliamentary scrutiny".
Backbench Tory MP David Davis has also accused the government of trying to stifle debate in the Commons with the use of a Statutory Instrument.
Baroness Smith pointed out that Conservative Lords behaved in a similar way to prevent the then-Labour government from increasing the National Insurance upper earnings limit without introducing further primary legislation.
- So are the plans likely to go through?
The Tories do not have a majority in the Lords, and many opponents of the cuts hope this might mean they are flatly rejected and so go no further.
It seems unlikely that the plans will be killed off altogether, however, as a 'fatal' motion was tabled by the Liberal Democrats at the Commons stage, but failed to win support from Labour.
Instead, Labour wants crossbench peers to back its bid to block the plans until further consultation is carried out. The shadow government has also demanded "full transitional protection" for low earners for at least three years.
Church of England bishops have also tabled a motion expressing "regret" over the impact of the cuts, without preventing its passage through parliament.