Staff at Allied Irish Banks (AIB) have threatened industrial action if management plans to change pay, pensions and benefits go ahead.
The Finance Union, IBOA, said its members were virtually unanimous in their rejection of a pending cuts package, while an overwhelming majority were prepared to join in litigation to prevent the implementation of the proposals.
The union also claimed a substantial majority of its 8,000 members said they would take industrial action if the bank attempted to impose changes without proper negotiation and agreement with the union.
Larry Broderick, IBOA general secretary, said the result should provide a wake up call for AIB's senior management and for the Irish Government, AIB's predominant shareholder. But he would not reveal the exact figures of the ballot.
"As a responsible trade union, IBOA is willing to engage in negotiating an acceptable solution to these issues," Mr Broderick added. "Industrial action is always a last resort for us. However, our members have now given us a clear mandate to pursue such a course if the bank attempts to proceed without reaching agreement."
IBOA said AIB's senior management wanted to prolong a pay freeze in place since 2009 for at least two more years, to reduce pension benefits further, and to remove other modest benefits enjoyed by some staff.
A delegation from IBOA, led by the general secretary, will present a letter against the proposal to the AIB chief executive David Duffy and its board at its AGM. Mr Broderick said AIB needed to engage meaningfully with his union on a fair deal for those staff who would be essential to the future capacity of the bank to meet the very daunting challenges that lay ahead if AIB Group was to recover.
AIB said later that the bank's focus was on driving down the costs of running the business.
"We must continue our focus on reducing overall costs at AIB," a spokeswoman said. "We need to ensure that the cost base of the bank is more properly aligned to the operating performance of the group while also ensuring the future viability of the bank so that over time we can generate a return to taxpayers for their significant investment in the bank."
In a statement, AIB said that its executive committee had agreed that the pay and benefits review must be founded on a fair, equitable and tiered approach. It also revealed that the members of the committee are taking a 15% pay cut, which includes salary and allowances, while bank executives take a 10% reduction.