A senior Tory MP has said preserving the pensions triple lock will "bankrupt the nation" days after the government announced it was keeping the policy in place.
The triple lock guarantees the state pension will increase every April by whatever is higher out of inflation, earnings, or 2.5%.
It has been the subject of debate in recent months amid reports the government was considering watering down the commitment.
In his budget on Thursday, chancellor Jeremy Hunt said the cost-of-living crisis was harming "all pensioners", confirming the government would increase the state pension in line with inflation.
Watch: Is a UK state pension enough to survive on in retirement?
However Sir Edward Leigh, Tory MP for Gainsborough, told MPs in parliament on Tuesday evening during a debate on the Autumn statement that the guarantee should be reviewed.
"I benefit from the triple lock, but long-term the triple lock is utterly unaffordable and will bankrupt the nation," he said.
"Of course pensions this year should go up with inflation, but what happens next year or the year after, when we deal with inflation and earnings start rocketing up?
"Will pensions then keep pace with earnings? We have to be honest with people, and I think people are prepared to listen to Conservative governments who are prepared to take difficult decisions."
The state pension is increasingly expensive for the Treasury, making up 41% of the total welfare spending bill in 2020-21 according to the Office for Budget Responsibility (OBR).
This figure is on the rise and set to increase further due to an ageing population.
OBR figures show the government spent £101bn in 2020/21 on the state pension - around 4.8% of GDP - considerably higher than 2010/11 when the government spent £70bn on the state pension, around 4.3% of GDP.
The triple lock has also been a key manifesto pledge for the Conservatives in recent years.
Pensioners tend to vote heavily Conservative. In 2019, YouGov found 67% of over 70s voted for the party.
Leigh's remarks come after older persons charity Age UK last week welcomed the government's decision to increase benefits in line with inflation.
“The restoration of the triple lock next year, uprating of pension credit in line with inflation, and cost of living payments, are all extremely important for older people, particularly for the many with no other income to fall back on, including hundreds of thousands of older women, and we welcome them wholeheartedly," said Caroline Abrahams, Charity Director at Age UK.
"We thank all the older people and their friends and allies who campaigned so hard for these things in recent months, and we thank the government for listening."