The dispute over Bank of Ireland plans to offer new staff a less attractive pensions package has been referred to the Labour Relations Commission.
The bank's main union, the IBOA, opposes the bank's plan to close its defined benefit scheme to new staff and offer a define contribution pension instead.
The IBOA's general secretary, Larry Broderick, said his members voted in a nationwide ballot to reject the bank's proposals, which he claims will leave thousands of young staff with an inadequate pension upon retirement.
"The bank's proposals in effect create a two-tier system within the bank, whereby staff undertaking the same job and on similar salaries will have totally different retirement packages with older staff able to retire on a pension of two-thirds final salary while younger staff will be left with a pension as little as one third final salary," Mr Broderick said.
He said there was "absolutely no justification" for the bank's actions and the proposals would cause "anger and deep resentment" among loyal staff throughout the bank.
Mr Broderick said that the IBOA has written to the Minister for Social Community and Family Affairs, Seamus Brennan, seeking an urgent meeting as the Bank of Ireland's proposals have "extremely serious consequences for future national pensions and taxation policy".