Christians Against Poverty (CAP) is urging the Chancellor to take action now to prevent more people falling into hardship this winter.
In a letter to Rishi Sunak, CAP asks that legacy benefit claimants - those receiving benefits like income-related Job Seekers Allowance or Employment Support Allowance - be included in the £20 per week uplift to Universal Credit.
The call follows an increase in people reaching out to CAP with concerns about bills and debt as a result of changing personal circumstances during the pandemic.
"We welcomed the Government's swift action to strengthen the support available through the social security system at the outset of the pandemic," writes CEO Paula Stringer.
"This bold and positive intervention has enabled many families to stay afloat, so we welcome the news that it is likely to be kept, but families on legacy benefits must be thrown the same lifeline.
"The majority of households on legacy benefits are disabled, sick or carers. Disabled people were already more likely to be in poverty heading into the pandemic.
"In the face of higher energy bills, panic buying and the increased need to pay for internet access, this group is feeling the pinch more than ever."
CAP says that only around a fifth of its clients qualified for the extra money when the Government first announced the Universal Credit uplift back in April.
The letter to Sunak has been sent ahead of next week's spending review. If legacy benefit claimants are included in the uplift now, they will start to receive the extra money from next April.
CAP warns that the poorest and those who are sick or disabled are being worst hit, and should not be excluded from the uplift.
"Nine in ten CAP clients in receipt of legacy benefits are in the poorest 10% of UK households. 80% have a health condition or disability that means they are unable to work, and one in three have dependent children," the letter continues.
"The uplift would make a huge difference to legacy benefit claimants. We estimate it would reduce the number of households unable to cover their living costs by 20% and move hundreds of thousands closer to a sufficient budget."
Rachel Gregory, CAP's Social Policy Manager, said the increase would provide a "much-needed lifeline" to people "on broken, unsustainable budgets".
CAP is urging people to sign a petition asking the Chancellor to "keep the social security lifeline", which has so far garnered over 150,000 signatures.