Ulster Bank will face a full review of its operations by its parent company the Royal Bank of Scotland.
RBS said today that the review will be concluded by the end of next February.
In a statement issued today, €10.5bn of the bank's loans will be put into an internal bad bank and wound down over time.
The bank said it needed to ensure that Ulster had a viable future and a sustainable business model.
The announcement is not expected to have any impact on customers, and it is "business as usual", the bank claims.
Ulster is the largest bank in Northern Ireland and the third largest in the Republic of Ireland, with more than 1.9 million customers. It is also the last British-owned retail bank in Northern Ireland.
Ulster is already undergoing a swingeing restructuring to save costs, slashing its branch network from 214 to between 175 and 185 by the end of 2014 and cutting its workforce from around 5,800 full-time staff to between 4,000 and 4,500 by 2016.
The bank was hit hard by the financial crisis and the bursting of the property bubble, leaving it with hefty arrears and toxic property debts.
RBS will make a substantial loss this year as the faster run-down of assets in the internal bad bank will cause an accounting write-down of up to £4.5bn.
And when including one-off items and an additional charge of £250 million to cover redress for the mis-selling of payment protection insurance (PPI), RBS made a bottom-line loss of £634 million in today’s third quarter results.