Labour has condemned government plans to review universal welfare payments such as child benefit and the winter fuel allowance, which could be frozen.
Labour leadership candidate David Miliband accused the Conservative-Lib Dem coalition government of misleading the public over fuel payments.
And shadow work and pensions secretary Yvette Cooper said it was a "shocking betrayal of pensioners".
But Deputy PM Nick Clegg said no final decisions had been taken.
Apart from freezing some welfare payments, the government could also consider paying benefits to all, whatever their income, but "tapering" them so that the poorest in society get the most money.
But government sources have indicated that "means testing" or ending the universality of such benefits will not happen.
Ministers are already committed to raising the age at which the winter fuel allowance can be claimed from 60 to 65 by 2020.
However, the government has not ruled out bringing this change forward.
Mr Miliband said: "David Cameron said that Labour was telling lies when we said their plans would mean they would have to hit winter fuel allowance.
"It turns out we were right. And we've got to say very clearly this is not the new politics, it's the old politics. And we've got to say very clearly, it's wrong.
"Up and down Britain, pensioners rely on this benefit to get by.
"The payments Labour introduced mean many pensioners can heat their homes without worrying and fretting over the energy bill to come. The prime minister's dishonesty is unacceptable."
Dot Gibson, general secretary of the National Pensioners Convention, also warned against changing the winter fuel allowance system.
She said: "Last winter over 36,700 pensioners died of cold-related illnesses - a staggering 13 pensioners every hour.
"Yet the government is now considering taking the winter fuel allowance away from millions of households which will only make matters worse."
Newspaper reports suggest the government will cut back universal payments such as the fuel allowance and child benefit, as part of a £13bn reduction.
But Deputy Prime Minister Nick Clegg, speaking as the coalition marked 100 days in power, dismissed the idea as "speculation" and refused to be drawn on the coalition's plans.
He told the BBC: "We are engaged as a government in a collective effort to get this right to both make savings to the welfare bill and to create a simpler, fairer welfare system that, above all, gets people into work."
The Times and The Daily Telegraph both report that the winter fuel payment could be reduced by as much as £100 in the government's comprehensive spending review this October.
Currently anyone over 60 is eligible, with households getting £250. Pensioners aged over 80 can claim £400 per household.
The scheme costs taxpayers about £2.7bn.
Child benefit, paid at the rate of £20.30 a week for the first child and £13.40 for other children, costs about £4.3bn a year.
BBC chief economics correspondent Hugh Pym said total spending on welfare, excluding state pensions, will be about £115bn - more than health, which costs £106bn, or any other department.
This figure means welfare is a tempting target for the spending axe, our correspondent added.
A Department for Work and Pensions spokeswoman said there would be no "running commentary" on the coalition's benefits plans.
She said: "The qualifying age for winter fuel payments for men and women is rising in line with the increase in women's state pension age.
"This is a gradual process. Under the current system women's state pension age is rising from 60 to 65 between April 2010 and April 2020. We have launched a call for evidence on raising state pension age to 66 and will publish our response in the autumn."
No decisions had yet been made ahead of the autumn's spending review and subsequent white paper on welfare reform, she added.
The coalition agreement pledges to "protect key benefits for older people such as the winter fuel payment", but does not rule out reform.