Free bus passes and prescriptions must be axed for better off pensioners, a close ally of David Cameron insists.
Tory moderniser Nick Boles also wants other universal benefits, such as free television licences for the over 75s and winter fuel payments, to be means-tested from 2015, arguing older people must shoulder their fair share of spending cuts.
The MP, who is said to be part of the prime minister's inner circle, concedes it will be politically difficult but insists that the government must admit it cannot continue to protect the payments after the next election.
In a speech to the independent think tank, the Resolution Foundation, Mr Boles will say: "If we are to achieve stability in our public finances and make crucial investments in improving productivity and competitiveness, we must find further savings from the welfare budget.
"And if we are going to protect spending on pensions - as we should - equity between the generations requires that these cuts cannot only fall on adults of working age.
"We need to acknowledge now that we will not be able to continue the protection of these other benefits for better-off pensioners after 2015.
"The coalition is going to be confronted with some very hard choices on public spending - in government the Conservatives and Liberal Democrats have already shown that we are willing and able to grit our teeth and take unpopular decisions in what we believe is the national interest.
"Is the current leadership of the Labour Party willing and able to do the same? We know what cuts Ed Miliband and Ed Balls oppose but very little about those they support. We know what further spending they would like to see but very little about the taxes they would raise."
Mr Cameron has insisted he will not touch the benefits during this parliament but work and pensions secretary Iain Duncan Smith last month suggested that commitment would be reassessed in the run up to the next election.