Boris Johnson has been urged to give millions of families a “helping hand” ahead of a Commons vote on extending benefit increases worth £20 a week.
Labour will use a debate on Monday to ramp up the pressure on the government to prolong the Universal Credit uplift, worth £1,000 a year, beyond 31 March.
Sir Keir Starmer said families “needed certainty” incomes would be protected.
Tory MPs will abstain, meaning the non-binding motion will pass but ministers have not committed to implementing it.
Work and Pensions Secretary Theresa Coffey said the government had “consistently stepped up” to support low-income families and the most vulnerable in society throughout the pandemic and would continue to do so.
And, speaking on Sunday, Foreign Secretary Dominic Raab said the rise was supposed to be temporary when it was introduced in April and March’s Budget would look at welfare support for the most vulnerable “in the round”.
Charities and anti-poverty campaigners are pleading with the government to keep the support in place, describing it as a lifeline for the more than 5.5 million families who receive the standard Universal Credit allowance.
Labour’s motion calls for this and the £20 weekly increase in Working Tax Credit also put in place at the beginning of the pandemic to be extended indefinitely beyond 31 March.
Sir Keir said it was a vital safety net for those who had lost their jobs, seen their working hours slashed or who were not eligible for the government’s wage subsidy furlough scheme.
“Without action from government, millions of families face a £1,000 per year shortfall in the midst of a historic crisis,” he said.
“If we don’t give a helping hand to families through this pandemic, then we are going to slow our economic recovery as we come out it.
“We urge Boris Johnson to change course and give families certainty today that their incomes will be protected.”
The Joseph Rowntree Foundation has suggested about 16 million people will be directly affected if the £20 is rolled back, with millions of households facing an income loss equivalent to £1,040 a year.
It says 500,000 more people will be driven into poverty, including 200,000 children, while a further 500,000 of those already in poverty will find themselves in even worse hardship.
Labour’s motion is sure to pass after Conservative MPs were told to abstain, amid fears that some – including those in “Blue Wall” seats in northern England elected last year – may defy the whip and vote against the government.
Speaking on behalf of the Northern Research Group, Conservative MP John Stevenson said the £1,000 uplift had been “a real life-saver for people throughout this pandemic”.
“To end it now would be devastating for the 6 million individuals and families who are already struggling to stay afloat,” he added.
While the vote is not binding, and will not lead to a change in policy, it will increase pressure on the government to either roll over the uplift or come up with an alternative.
Labour said the Conservatives’ decision to abstain created “unnecessary uncertainty” but Mr Raab said the debate was a “political” move by the opposition.
The government says it has strengthened the welfare system with an extra £7bn of funding during the pandemic while families struggling with food and household bills can get help through the £170m Winter Grant Scheme.
Ministers also point to extra support for housing costs, through an increase in local housing allowance for those on housing benefits and hardship payments worth £670m next year for those unable to pay their council tax bills.
Mr Raab said Chancellor Rishi Sunak would be taking a “holistic” approach to the support on offer in the Budget scheduled for 3 March.
“We’ve put that support in place to make sure that the most vulnerable communities can be protected at this very difficult time,” he told the Andrew Marr show.