RBS-owned Ulster Bank has confirmed it is cutting 950 jobs from its branches on both sides of the Irish border - a far higher figure than predicted on Wednesday.
The bank said 600 posts would go in the Irish Republic and 350 would be lost across Northern Ireland. It said it could not rule out compulsory redundancies.
Ulster Bank blamed the deterioration in the Irish and global economies for the cuts and said it needed to make the move to maintain a presence in the Irish banking market. It said it had no plans at present to reduce the number of branches on either side of the border but that would be kept under review.
The Irish Bank Officials Association (IBOA), the finance sector union, said it was alarmed by the scale of the proposed job cuts.
The IBOA said it would seek a "detailed analysis from management" of the rationale for the planned redundancies.
The job losses are part of a larger rationalisation by its parent group Royal Bank of Scotland, which earlier announced around 3,500 job losses over the next three years.
Ulster Bank has 1.9 million customers in the republic and Northern Ireland, and employs 6,000 staff.
The announcement signals the second round of redundancies that the lender has undertaken since the Irish banking crisis began in 2008. The bank cut 1,000 jobs in 2009.
