SIPTU is set to ballot its members at Dublin Bus and Irish Rail for industrial action in sympathy with their colleagues in Bus Eireann.
ollowing a meeting of representatives from the three CIE companies today, the union said it had a mandate for the vote because members believe they are "next in the firing line" if Bus Eireann forces through pay cuts and changes to terms and conditions.
The meeting was called after workers mounted an all-out strike last Friday after the company announced it would impose cuts to earnings in a bid to lower its payroll costs by €12m.
Acting Chief Executive Ray Hernan has warned that the company faces insolvency in May.
The union representatives also discussed a planned protest in support of the Bus Eireann workers to be held at Leinster House on Wednesday to coincide with a meeting of the Oireachtas transport committee that Minister for Transport, Shane Ross, is due to attend.
SIPTU Sector Organiser, Willie Noone, said that if Bus Eireann becomes insolvent and 2,600 people have no jobs, their CIE colleagues are "not going to sit back and take that".
He said the representatives agreed that Wednesday's protest should be supported as it is a means of highlighting the "failure" of the minister to take responsibility for the "dysfunctional state" of the public transport service.
"We are encouraging members of the public and of the union, including those who work in the public transport sector and are available, to attend the protest," said Mr Noone.
Earlier, Bus Eireann revealed it will not be able to fund a voluntary redundancy scheme and will have to "consider other measures" to avoid becoming insolvent.
The board today discussed a management plan to cut 300 jobs through an exit scheme under a €30m cost-cutting plan at a crucial meeting to sign off on its accounts for last year.
Following the meeting, it said it was unable to sign off on its accounts and could not pass a budget for next year "in the absence of agreement with staff."
"This is a very serious matter as the board must now formally advise CIE that this governance requirement will not be met," it said in a statement.
It said management had presented the board with a plan that will secure the future of the company and a key component of this was cost efficiencies to eliminate "grossly inefficient" work practices.
The statement said these inefficiencies had been acknowledged by unions at talks at the Workplace Relations Commission.
It said management had presented the Board of Bus Éireann with a plan which will secure the future of the company.
"The board remains gravely concerned that losses continue to accelerate at Bus Éireann, exacerbated now by four days of strike action," it said.
"Regrettably, today the board could not sign off accounts for 2016, or pass a budget for 2017 in the absence of agreement with staff.
"Without a plan which encompasses the necessary work practice changes to generate savings, it will not be possible to fund a voluntary redundancy scheme and faced with that scenario, the board of directors will have no option but to consider other measures to prevent the business becoming insolvent."
It urged all employees to urgently engage in talks with management through their unions to agree a survival plan.
Meanwhile, the General Secretary of the National Bus and Railworkers Union, Dermot O'Leary, has warned against the consequences of compulsory redundancies following the company's comments.
He described the company's statement as "bizarre and extraordinary" given that 2,500 staff have been on strike for four days in response to the imposition of cuts.
"The notion that alternatives to work practice changes and a voluntary severance programme would be entertained, would appear to indicate that the company may go down the road of compulsory redundancies which, if pursued would be unprecedented in the semi-state sector," he said.
He said compulsorily laying off staff will "open a completely different and potentially uncontrollable" dimension to the dispute and present severe difficulties maintaining the "already fragile" industrial peace across other CIE companies. He said the NBRU is fully prepared to engage in talks on efficiencies.