Rail users are bracing themselves for travel chaos with workers gearing up for strike action.
General Secretary of the National Bus and Railworkers' Union (NBRU), Dermot O'Leary, told members at his union's annual conference that industrial action over a pay claim will happen as early as next month.
Earlier, he said that his members would hold an immediate ballot unless Irish Rail made a "tangible" offer, after demanding a 3.75pc-a-year wage hike.
This was the same increase given to Luas and Dublin Bus drivers.
He revealed the union has also written to Bus Eireann warning that it is heading towards a potential stand-off that could result in more industrial action by the end of October due to a row over rosters.
The union chief said any attempt by the CIE companies to impose changes to pensions could lead to industrial action that "would have catastrophic consequences" for the entire transport network.
Mr O'Leary picked out Irish Rail chief executive David Franks for stinging criticism.
"Unless a tangible offer is made, unless something substantial is on the table, the NBRU will not be a party to abusing the good offices of the Labour Court by going back and asking it to do the impossible," he said.
"The only alternative open to us at this juncture will be to undertake an immediate ballot for industrial action across our railways. Let us then see how Mr Ross and his fellow cosseted Dublin-based TDs will explain to their constituents how it is that their trains are not running."
Unions are due to meet Irish Rail negotiators at the Workplace Relations Commission next week to discuss the pay claim.
Meanwhile, Bus Eireann said it will discuss the NBRU concerns regarding rosters in a meeting next week.