Controversy over the 50p income tax rate is set to be fuelled with the announcement that top earners are to be targeted by a dedicated team of tax inspectors.
Chancellor George Osborne has ordered a review of whether the higher levy is justified by the amount of extra revenue it generates, saying "inefficient" taxes are pointless.
In his conference speech, his Liberal Democrat Treasury colleague Danny Alexander said that a 100-strong "affluence team" was being employed to make sure the richest were paying up.
It will concentrate on the 350,000 people in the UK whose personal wealth is more than £2.5 million.
The Chief Secretary to the Treasury told the Independent on Sunday that the move had been "driven forward" by the Lib Dems and would target "particularly people who might be eligible to pay tax at the 50p rate".
"We are keeping up the pressure on tax evasion and tax avoidance, on making sure that those with the broadest shoulders bear their fair share of the burden," he said.
The unit is being drawn from 2,250 newly-recruited tax inspectors expected to be in place within weeks.
Mr Alexander said scrapping the 50p rate was "just so much the wrong priority" and turned one of Mr Osborne's pre-election soundbites back on the Chancellor.
"We are having to take some very, very difficult decisions that are affecting everybody in the country. We are all in this together, and that means particularly ensuring that those with the broadest shoulders bear the greatest share of the burden."