Media speculation suggests that the Financial Regulator has sent a team of investigators into the head offices of Irish Nationwide.
Around half a dozen inspectors appointed by the regulator are on site at Irish Nationwide's head office and are examining documents there.
The reports suggest that the inspectors have wide powers which allow them to see any documents they want to without having to go to the courts.
The officers include staff from top accountancy firms Deloitte, Pricewaterhouse Coopers and KPMG.