AIB's operation in Northern Ireland, known as First Trust, is to close half its branches.
While the bank has not specified the job losses the Financial Services Union said there would be a minimum of 130 employees affected.
The redundancies will be voluntary.
General Secretary of the Financial Services Union, Larry Broderick, said it was "a serious blow for staff, customers and the Northern Ireland economy."
He added: "While opposing the scale of the closures, the Financial Services Union, will work hard over the coming months to ensure that commitments made to staff are upheld."
AIB trades under the name First Trust in the North.
The bank said in a statement its "transformation programme" would involve the closure of 15 of its 30 branches.
However, it said it would make a £10m investment to service personal and business customers.
It said since 2010 the bank had seen an almost 40% decline in branch usage coupled with 117% increase in mobile transactions.
The bank has agreed a partnership with the Post Office which will enable customers carry out transactions.
It said it was making the changes to address "the considerable shift in customer behaviour and their changing needs."
The affected branches will be closed by the end of July.
AIB is preparing for a stock market flotation and will announce full-year results next month.