Iarnród Éireann says it regrets the decision of the NBRU to reject a Labour Court recommendation on cost reduction at the company.
Up to 75% of NBRU members today voted against the measures.
Last week, SIPTU staff at Irish Rail rejected the Labour Court recommendation, but the TSSA, TEEU and Unite accepted the proposals.
Irish rail says it is now giving immediate consideration to what course of action to adopt, given the urgent need to achieve cost savings, and the acute threat to the financial solvency of Iarnrod Eireann.