The Government has been called on to force the mortgage lender Permanent TSB to reduce the interest rate it applies to mortgages.
Fianna Fáil's deputy leader Eamon O'Cuiv says the variable rate of 5.1% being charged by the bank is "despicable".
"People are trapped with this mortgage-holder, because if you're in negative equity, you can't move to another lender…They won't lend you the money," he said.
"I think it's despicable behaviour on the part of the PTSB that they are charging these rates."
He said the rate should be brought in line with the AIB rate of 3% in a bid to help hard-pressed homeowners.
Tánaiste Eamon Gilmore said the Government shared Deputy O'Cuiv's concerns, but that it was a matter for the regulator.
"We are anxious to ensure that there is no discriminatory practice between one customer and another. The financial regulator's job is to deal with the institutions in respect of this," he said.