SIPTU will begin counting votes from a ballot cast by its members at Irish Rail later this morning.
Workers are voting to either accept or reject new terms relating to proposed pay cuts and cost saving measures at the company.
Irish Rail staff want assurances that if Government funding is cut, it won't affect pay.
If these proposals are rejected and Irish Rail is unwilling to negotiate further - industrial action will proceed, as it has already been approved by a two-to-one majority.