Permanent TSB plans to lay off 300 employees as part of its ongoing restructuring.
In December, the bank revealed a voluntary exit scheme, initially available to Senior Managers in October, would be expanded to include all staff.
The Financial Services Union intends to meet the bank in the coming weeks to seek clarification on the rationale behind each redundancy.
Gareth Murphy, FSU's head of industrial relations, said they are concerned about customers and impacts on job losses.
"We're very concerned about 300 potential job losses at Permanent TSB. We're concerned for customers and the impact any job losses will have on services," he said.
"We're also concerned for remaining staff. While these redundencies, thankfully will be voluntary redundencies, we are worried about a potential increase in workload, job transfer, and work-related stress and pressure for the remaining staff."
