Wealthier retired people would lose their annual winter fuel payment under Liberal Democrat proposals to protect the “triple lock” on state pensions
The election manifesto vow would see those on incomes in the 40% tax bracket lose the allowance – worth up to £300.
But the Lib Dems said an extra £772 a year would be paid in pensions by 2021.
Labour has also pledged to retain the guarantee which sees the state pension rise in line with wages, inflation or by 2.5% – whichever is highest.
Prime Minister Theresa May has declined opportunities to confirm the Conservatives would guarantee the triple lock in their manifesto for the 8 June general election.
The triple lock was originally a feature of the Lib Dem manifesto in 2010 and a key demand when the party negotiated on the formation of the coalition government with the Conservatives.
Announcing its latest pledge, former Business Secretary Sir Vince Cable said: “Liberal Democrats believe that an important test of a civilised society is the way in which it cares for the elderly.
“The guiding principle of the pensions system must be to ensure that none are left unable to meet their basic needs for survival and participation in society, and that everyone is treated with the respect and dignity they deserve.”
Under the proposals, an estimated 600,000 pensioners with annual incomes above about £45,000 – 5% of those under 80 and 2% of over-80s – would lose the winter fuel payment, saving the Treasury around £105m.
Earlier, the Liberal Democrats pledged to raise an additional £6bn a year to improve the health and social care system with a penny-in-the-pound rise on all income tax bands and on dividends.
The triple-lock has seen pensioner incomes rise faster than average earnings since 2010.
A cross-party House of Commons select committee report earlier this year described it as “inherently unsustainable” and recommended it should not be continued beyond 2020.
A review by former CBI director-general John Cridland, who was appointed as the government’s independent reviewer of state pension age last year, also recommended the triple lock be withdrawn.
But as well as guaranteeing the triple-lock, Labour has promised to keep the winter fuel allowance, which is paid to all-over 65s and worth between £100 and £300 tax-free.
A Labour Treasury spokesman said: “You can’t trust the Liberal Democrats. Only in September their former leader Nick Clegg called for the triple lock to be dropped.
“For a party with so few MPs, they cannot agree with each other on anything, as we saw with tuition fees in the last parliament.”
A Conservative spokesman said: “Because of the strong economy we have delivered, Theresa May and her Conservative team have increased the basic state pension by £1,250.
“The real risk to pensions comes from Jeremy Corbyn propped up in a coalition of chaos by the Lib Dems and the SNP.”