Around 4,000 members of the National Bus and Railworkers Union will begin voting tomorrow on taking industrial action over the proposed restructuring of CIÉ.
The union warned today Christmas services could be hit if members vote for strike action.
The Minister for Transport Mr Seamus Brennan announced earlier this month that he intends to dismantle the State transport company and give independent status to Dublin Bus, Iarnród Éireann and Bus Éireann.
The NBRU's general secretary Mr Liam Tobin said this afternoon he will seek assurances from Mr Brennan that no changes will be introduced without prior agreement through the National Transport Forum. This was established under the Programme for Prosperity and Fairness.
He said the union accepted that there was an urgent need for change in public transport, but that privatisation was not the answer. It called for further Government investment in transport.
Mr Tobin added that industrial action would be used as a last resort in stopping the Minister from implementing changes without agreement.
The ballot is expected to be completed by early December.