SWANSEA West MP Geraint Davies has accused the Prime Minister of "taking from the poor and giving to the rich".
Mr Davies challenged David Cameron during the weekly Prime Minister's Questions.
He said: "The Office for Budget Responsibility tells us that the bankers will pay £500 million less for the bankers tax than the Prime Minister promised last year, yet in April he will inflict a £500 million cut on the poorest through the second empty bedroom tax.
"How can he justify taking from the poor and giving to the rich?"
In response, Mr Cameron said the Government had introduced the bank levy.
He added: "We think that that is a better answer than a one-off bonus tax. The bank levy will, of course, be paid every year, so it will raise considerably more than a one-off bonus tax.
"What my right honourable friend the Chancellor has done when the bank levy has not come up to the figures that we require is increase the bank levy to make sure that they do."