Ulster Bank says it will close "in the region" of 20 branches and sub-offices in Ireland this year.
In a statement this afternoon, the bank said it will provide further details on the closures to customers and employees within the next few weeks.
The Irish Bank Officials' Association will meet the bank next week, having learned of the closures during a staff conference call last week.
The bank has 146 branches in the Republic of Ireland and 90 in Northern Ireland.
IBOA general secretary Larry Broderick said: "I'm shocked that an announcement like this was made during a teleconference with no prior consultation with our union.
"In light of this, the bank has agreed to meet us next week,'' he added.
Royal Bank of Scotland, which owns Ulster Bank, has injected at least £10.8 billion into the bank since 2008 to absorb losses after the property market downturn.
Ulster Bank's operating loss widened in the first nine months of last year to £797m from £751m the same time in 2011, as a fall in interest income offset stabilising loan losses.
Meanwhile, a separate IBOA notice to Ulster Bank members in November said the unit's chief executive officer Jim Brown told the union that RBS remains committed to its Irish unit. Ulster Bank said last year it will eliminate 950 jobs.
RBS acquired Ulster Bank in 2000 as part of its purchase of National Westminster Bank and expanded three years later through the acquisition of the First Active building society.