Plans to axe the disability living allowance (DLA) and replace it with a personal independence payment (PIP) will mean most recipients are reassessed.
A survey carried out by the charity Papworth Trust found 86% of disabled people would have to cut down on essentials if their payments were stopped or reduced.
The main area claimants said they would have to scale back their spending was on items such as food and drink, closely followed by utility bills and specialist transport.
Of the 2,200 people surveyed, three-quarters believe the Government is penalising disabled people unfairly.
Government officials insist that DLA payments are for additional living costs such as increased transport costs or care fees, not food or utility bills.
Claimants can receive up to £125 a week if they are eligible for the higher rate mobility and care element of DLA.
Papworth Trust chief executive Adrian Bagg said: “We know that all parts of society are facing cuts. Our survey shows that for 5% of disabled people these cuts would have little or no effect, but given the Government is seeking a 20% reduction, this will mean real-terms cuts that further disadvantage many disabled people.
“The people who participated in this survey have many concerns about the proposed changes, but they are particularly anxious that the new PIP Assessment will be unfair.”
Mr Bagg urged the Government to “learn the lessons” of previous benefit reforms and “ensure that if they make this change, the assessment will be fair and the implications clearly explained”.
The Government says it is too soon to say how many people will be affected by the introduction of PIP as the assessment process is still being developed.
It insists the reforms are needed as 70% of DLA claimants are eligible for payments for life without any reassessment.
The benefit costs £12 billion a year, more than the Department for Transport’s annual budget, and the Government is planning to save around 20% on working age claimants’ bill by 2015/16.
A Department for Work and Pensions spokesman said: “We have been clear that disabled people who need support will get it.
“However, we know that as well as millions of pounds in overpayments, lots of disabled people are being underpaid because of the inefficient DLA system.
“That is why we are introducing an objective assessment and regular reviews – something lacking in the current system – to make sure people are getting the right levels of support.”