Irish Rail drivers will meet today to decide what form of industrial action they will take.
SIPTU and The National Bus and Rail Workers Union voted overwhelmingly on Monday for industrial action in a dispute over payment for past productivity.
Members of SIPTU voted 92% in favour, while members of the NBRU backed the strike by 95%.
SIPTU Organiser Paul Cullen said they had done all they could to resolve this issue.
"We have desperately tried to find a resolution to this. We need the company to come to the table and discuss this," he said, saying discussions had been underway since before December 2014.
Irish Rail described the threat of action as "ridiculous", insisting company was willing to sit down to negotiate with workers on their concerns.
Unions have not confirmed when the action is likely to happen, but said it would be within weeks rather than months.