Deputy PM Nick Clegg has suggested the UK's wealthiest people could be asked to pay more tax for a limited period.
He said that "if we want to remain cohesive and prosperous as a society" those of "very considerable" wealth should make an extra contribution, in an interview with the Guardian.
"What we are embarked on is in some senses a longer economic war rather than a short economic battle," he said.
He also hinted at a return to cabinet for ex-treasury minister David Laws.
Liberal Democrat Mr Laws resigned as chief secretary to the Treasury two years ago after admitting he claimed expenses to pay his partner rent.
"I have never made any secret of the fact that I want to see David Laws back in government," Mr Clegg told the newspaper.
He also said the coalition would stand by its commitment not to build a third runway at Heathrow despite growing calls from Tory MPs for a change of heart.
'Belt tightening'In the Guardian interview, he called for a "time limited contribution" from the richest in society beyond his party's current policy for a mansion tax - taxes on properties above a certain value.
"In addition to our standing policy on things like the mansion tax is there a time limited contribution you can ask in some way or another from people of considerable wealth so they feel they are making a contribution to the national effort?" he said.
"What we are embarked on is in some senses a longer economic war rather than a short economic battle."
But he said fairness was key to the next steps in tackling the economic downturn.
"If we are going to ask people for more sacrifices over a longer period of time, a longer period of belt tightening as a country, then we just have to make sure that people see it is being done as fairly and as progressively as possible," he said.
"While I am proud of some of the things we have done as a government I actually think we need to really hard-wire fairness into what we do in the next phases of fiscal restraint.
"If we don't do that I don't think the process will be either socially or politically sustainable or acceptable."
'Failing plan'Responding to the interview, Chris Leslie, Labour's shadow treasury minister, said: "Nick Clegg is once again taking the British people for fools. He talks about a tax on the wealthiest, but he voted for the tax cut for millionaires in George Osborne's Budget.
"And he has supported a failing economic plan which has pushed Britain into a double-dip recession and is leading to borrowing going up by a quarter so far this year."
A Lib Dem source played down any suggestion of an imminent policy announcement, and suggested the party was likely to have a combination of measures in mind.
Discussions about tax and spending will take place before the chancellor's autumn statement.
