The pensions "triple lock" - which guarantees yearly pension rises of at least 2.5% - must be scrapped after 2020, MP Frank Field has said.
The Work & Pensions Select Committee chairman told the BBC keeping the guarantee could cost the taxpayer an additional £50bn by 2050. It would mean raising the retirement age to beyond 70, he said.
The "triple lock", implemented by the Conservative-Lib Dem coalition government under David Cameron, guarantees pensions rise by the same as average earnings, the consumer price index, or 2.5%, whichever is the highest.
Retirees told BBC Radio 5 the guarantees were needed to ensure people had enough to retire on. "So many pensioners are not well off... And thanks to age discrimination and automation I'm not sure what jobs would be available for people over the age of 70 [to top up their incomes]," one caller said.
But Field argued the cost of keeping it would fall on younger, working age people - many of whom could be "reduced to destitution".
Pensions minister at the time the policy was implemented in 2010, Steve Webb, said scrapping it in 2020 would be a bad idea.
"The reason it was brought in was that for 30 years the value of the pension had been eroded. It was just linked to prices and that meant as everyone's average wages were going up, pensioners were being left behind.
"Most state pensioners today get £119 a week, bear in mind that most don't have generous private pensions [to top this up]."