The UK's leading charity for older people has said millions will be left with "no chance of making ends meet" if the government fails to keep its promise on the pensions triple lock.
Age UK warned any backtracking by Rishi Sunak would be regarded as a "blatant breach of faith" and that people wouldn't be able to believe a "word any of them say".
On Thursday, Downing Street acknowledged there is uncertainty on whether the triple lock for state pensions will be maintained, despite Sunak promising to stick to the 2019 election manifesto on Tuesday.
Sunak is faced with trying to fill a reported £50bn black hole and is expected to unveil public spending cuts and higher taxes in the coming weeks.
He has pledged to "fix" the mistakes of Liz Truss, with chancellor Jeremy Hunt warning decisions of "eye-watering difficulty" ahead on tax and spending.
The pension triple lock guarantees that state pensions grow each year in line with whichever is highest out of: earnings, inflation or 2.5%.
Caroline Abrahams, director at Age UK, has warned that a failure to uphold the triple-lock would be devastating for millions of pensioners already living on the breadline during the cost-of-living crisis.
"The physical health effects on those affected would be severe but, if anything, the psychological impact would be even worse, due to the acute stress and anxiety this would cause," she told Yahoo News UK.
"We are already hearing from older people who say they don’t think they will survive the next few months; we’re clear that abolishing the triple lock would mean we’d hear from many more."
Recent data shows that poverty among pensioners is growing, with data analysis from Centre for Ageing Better in March revealing one in five pensioners live in poverty - an increase 200,000 on the previous year.
Abrahams also emphasised that the government's 2019 manifesto promised to protect pensioners from any cuts to their pensions, and warned there would be "political consequences" if they reneged.
"The 2019 Conservative manifesto pledged to keep the triple lock during this parliament and our new prime minister has said his intention is to implement it - indeed his party has said this is why there is no immediate need for a general election," she said.
"In addition, his immediate predecessor, Liz Truss, very publicly pledged to abide by the triple lock just last week.
"If Rishi Sunak decides to ditch the triple lock now, older people would be entitled to conclude that they can’t believe a word any of them say. It would indeed be a blatant breach of faith.”
It comes as Labour calls for a general election, warning that breaking manifesto pledges - including the pension triple-lock - betrays the mandate the government were given by the public.
"If the argument that Conservatives are making is ‘The things we promised in our last manifesto can no longer be afforded because we crashed the economy’, then I think they have a responsibility to go back to the voters and ask them for permission for the plan that they want to pursue in order to fix the damage they’ve done," said shadow health secretary Wes Streeting on Thursday.
“We will happily compare our plan with this and let the people decide.”
Watch: Is a UK state pension enough to survive on in retirement?