Lib Dem leader Nick Clegg has insisted he will not sanction further spending cuts without the coalition backing new taxes on the rich.
Mr Clegg, speaking from the party conference in Brighton, suggested a crackdown on tax avoidance by wealthy homeowners was the tip of the iceberg.
"The vast majority of people in this country won't find it acceptable if further fiscal austerity was implemented on the backs of the poor," he said.
"I'm not saying something as big as welfare is immune from further savings but I'm saying that the burden has to be spread fairly."
The Lib Dems look set to make some kind of wealth tax the price of their support for accepting billions in extra cuts in the next spending round for 2015-16.
Mr Clegg admitted "so far I have failed" to persuade David Cameron and George Osborne to accept his party's favoured mansion tax.
But he told the BBC's Andrew Marr show: "The mansion tax is not the only way in which you can make people at the top make a fair contribution to this huge national effort of balancing the books."
Asked if he believed he could persuade the Tories to back a wealth tax, he said: "I think there is a very considerable chance, because we have already done a lot of it, to make sure that the top pay more tax.
"We have already illustrated through capital gains tax, through stamp duty, through tax avoidance and many other measures ... the top 10% pay more and we can do more of that."
Under the existing new tax plans, anyone with assets worth more than £1m are to face greater scrutiny from inspectors to make sure they are paying the right tax.
The move, part of a drive led by the Lib Dems as they seek to boost their popularity, will mean 500,000 people in total being targeted.
An extra 100 officials will join the HM Revenue and Customs' affluence unit to help "sniff out" people who flout the rules.
The Lib Dems have also revealed a new bid to help young people get on the housing ladder by allowing parents and grandparents to draw on their pension pots to secure deposits.
They will be able to release a tax-free lump sum when they quit work and use it to guarantee part of a mortgage for their children or grandchildren.
Chief Secretary to the Treasury, Danny Alexander, explained: "There are a lot of people out there who already help their children with deposits. That happened to me when I bought my first home.
"But there are an awful lot of parents out there who don't have any cash to help their children get on the housing ladder. But in many cases they will have built up a substantial pension pot."
With fairer taxes the theme of the Brighton conference, Business Secretary Vince Cable has indicated he wants a fresh assault on tax havens and non-domicile millionaires.
He told the Sunday Times he wants tough action against "shady" wealthy people who make "systematic and cynical" use of offshore havens.
The Liberal Democrats are battling to regain popularity amid dire ratings in the polls. A new survey on Sunday put the party in fourth behind Ukip on just 8%.
Mr Clegg's leadership is also under increasing scrutiny amid rumours of rivalry as his personal popularity continues to plummet.
In a bid to restore the party's fortunes, he has apologised publicly for the U-turn on tuition fees and admitted on Saturday that the Lib Dems had made mistakes in coalition.
But he stressed it was only "half-time" in their term in office and rubbished suggestions that he will step down before 2015.
Shadow chief secretary to the Treasury Rachel Reeves claimed the public would not be taken in by Mr Clegg's "empty words" on tax.
"This is the man who backed a £3bn tax cut for millionaires in the Budget while asking millions of pensioners and families to pay more," she said.
"There's nothing fair about a family with children paying an average £511 extra from changes the Government has brought in this year, while millionaires will get a £40,000 tax cut next year.
"Nick Clegg is the Deputy Prime Minister of this Government and he must take responsibility for its actions. After so many broken promises, people will judge the Liberal Democrats on what they do, not what they say."
