Labour MP Stephen Timms has described a £20 cut to universal credit as "unthinkable".
It is estimated a cut to the benefit will hit more than 17,000 families in Mr Timms's East Ham constituency.
More than 350 Conservative MPs refused to side with Labour's bid to thwart the government's plan to cut the benefit by more than £1,000 a year in a House of Commons vote on Monday, January 18.
%image(15260836, type="article-full", alt="Stephen Timms MP described the withdrawal of support as "unthinkable".")
Mr Timms, speaking after the vote, said: "It is unthinkable that Conservative MPs are pulling away support from families in East Ham in the midst of an economic crisis. This was a missed opportunity for the government to give them the certainty and security they deserve."
He added the government can still do the right thing and drop its plan.
"I will continue to press ministers to do the right thing and keep the £20 uplift and ask that those on legacy benefits – such as employment and support allowance and jobseekers' allowance – be uprated in line with those on universal credit too. The government has consistently refused to do this," Mr Timms said.
Universal credit was raised by £1,040 for the 2020/21 financial year to help with the impact of the coronavirus pandemic. At the time, ministers said the increase would only be temporary.
%image(15260841, type="article-full", alt="Prime Minister Boris Johnson has refused to rule out cutting the benefit.")
Boris Johnson refused when asked if he would provide certainty to families and cancel the cut at a liaison committee hearing in Parliament on January 13.
The prime minister said: "What we want to see is jobs. We want people in employment and we want to see the economy bouncing back.
"Most people in this country want to see a focus on jobs and growth in wages than on welfare, but clearly we have to keep all of these things under review."
Labour's non-binding motion pressing the government to maintain the increase was approved by 278 votes to zero after Mr Johnson ordered his MPs to abstain.
However, six Conservative MPs rebelled to support the motion, including senior Tories Stephen Crabb and Robert Halfon.
Downing Street has insisted no decision has been made on whether to keep or scrap the increase, and said the chancellor, Rishi Sunak, will update the public on the government's plans "shortly".
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