Raising income tax allowances is "literally twice as good" as bringing back a 10p rate, Nick Clegg is to say as he seeks to counter Labour's challenge on help for squeezed workers.
The deputy prime minister will dismiss Ed Miliband's backing of a "mansion tax" on £2 million properties to pay for a return of the lower rate scrapped by Gordon Brown as a "pale imitation" of his party's policies.
Chancellor George Osborne is under pressure from some Conservative backbenchers to restore the 10p rate in next month's Budget - or find other ways to ease the pressure on household budgets.
And Miliband is also seeking to split the coalition with a Commons vote forcing the Lib Dems to choose between backing its cherished mansion tax policy or maintaining unity with the Tories.
Business secretary Vince Cable indicated that colleagues would want to support a motion purely on the property levy but expected Labour to link it to the income tax change, enabling Lib Dems to oppose it.
In a speech at the Mansion House in the City of London, Clegg will say: "We have waited two and a half years for Labour to apologise for messing up the economy and to come up with some new ideas on how to fix it.
"But all we've got from Ed Miliband last week is some blatant plagiarism of Liberal Democrat ideas and still no remorse for the biggest economic meltdown in modern times.
"Labour cannot be taken seriously until its leaders apologise for the economic mess they created, apologise for the unfair tax system they left behind, and apologise for letting tax avoidance rip."
He will go on: "In the meantime, it is the Liberal Democrat commitment to tax fairness which is dominating the debate.
"We have cut in half the income tax bill for people working full time on the minimum wage. From April this year, more than 20 million people will have had a £600 tax cut, and more than two million will have been lifted out of paying income tax altogether.
"Paying no tax at all is far better than a new, complex 10p rate. Our policy is literally twice as good as theirs. Someone who paid only the 10p tax rate until Labour doubled it, has now been lifted out of paying tax altogether.
"If it's fairer taxes you want, the Liberal Democrats are the real thing, and Labour a pale imitation."