Liberal Democrat treasury spokesman Vince Cable has lashed out at the "nauseating" behaviour of business chiefs who backed the Tories' promised national insurance cut.
In an interview with The Guardian, he accused the more than 130 business leaders who publicly came out in favour of the Conservative plan of allowing themselves to be "used" by the Tories.
He said that they now needed to explain properly how the cut in the Government's planned national insurance increase - due to come into effect next April - would be paid for.
"If they are going to wade into this debate, they do have an obligation to explain how this national insurance cut is going to be paid for and that is where they are failing and they are being used," he said.
"I just find it utterly nauseating all these chairmen and chief executives of Ftse companies being paid 100 times the pay of their average employees lecturing us on how we should run the country. I find it barefaced cheek."
Business leaders previously reacted angrily to suggestions by Gordon Brown and Business Secretary Lord Mandelson that they were "deceived" by the Conservatives.
Sir Stuart Rose, the Marks & Spencer executive chairman and one of the most prominent backers of the Tory plan, accused the Labour leadership of insulting the intelligence of the business community.
However Mr Cable - who was previously the chief economist for the oil giant Shell - was far more forthright in his condemnation of the business chiefs.
He said that Mr Brown should "hit back" against them, but was undermined by his previous efforts to enlist their support.
"Brown, having kow towed to the City for the best part of a decade, and having tried to co-opt captains of industry into the big tent, is in a very weak position," he said.