Talks are taking place at the Labour Relations Commission in a bid to avert industrial action at the EBS financial institution.
The dispute concerns the non-payment by management in 2011 of a traditional Christmas bonus for non-managerial staff known as the "13th month".
Management at EBS, which has since merged with AIB, argued that under a "placing agreement" dealing with remuneration in banks, the Government would not permit them to pay bonuses.
Earlier this year, the Labour Court ruled that the 2011 bonus should be paid in full, but should then be discontinued.
EBS has paid half the bonus, equivalent to two weeks' wages, but has refused to pay the other half until a range of "harmonisation" issues surrounding the merger of EBS and AIB are resolved.
The Unite trade union, representing up to 300 staff, has said it will not discuss harmonisation issues until the outstanding bonus is paid.
The union has threatened to issue notice of industrial action tomorrow if the LRC talks fail to resolve the row tonight.
Unite has also warned that if a one-day strike goes ahead, it may also place pickets on AIB branches, now that the two institutions have been merged.