The Sinn Féin spokesperson on Finance, Pearse Doherty, has written to the Governor of Central Bank to request the Bank to examine the practice of differential pricing in the mortgage market.
This is the practice whereby new customers are offered lower priced mortgages compared to higher rates for existing customers.
In his letter, Mr Doherty asks that the bank undertake work to clarify the extent of the practice, its impact on customers and its compatibility with the Consumer Protection Code.
The bank is currently undertaking a probe into so-called 'dual pricing' in the insurance market.
Mr Doherty claims what's going on in the mortgage market is 'another manifestation of this practice.'
The Fianna Fail spokesperson on Finance, Michael McGrath, has also raised the issue.
In a statement, Mr Grath said he had contacted the Competition and Consumer Protection Commission in relation to the practice and had also asked the Central Bank to intervene.