Unions representing transport workers will meet today to draw up plans for fresh industrial action that could begin within the next fortnight.
This is likely to include a series of rolling measures, such as more "no-fares" days, or conventional protests involving disruption of bus and rail transport.
The Minister for Transport, Mr Brennan, said last night he had written to CIÉ unions seeking to re-establish talks over his plans to break up the company. He said he was "strongly of the view" that the planned reforms could go ahead while protecting the terms and conditions of workers in CIÉ.
Earlier, the Taoiseach, also asked the unions to return to talks. Mr Ahern said large subsidies footed by the taxpayer could not continue without reform of the transport network. He also insisted that pay and conditions for employees would not be affected.
The National Bus and Rail Union (NBRU), which represents more than 3,000 workers in CIÉ, and SIPTU, as well as smaller unions, say the Mr Brennan's attitude to the talks made it impossible for them to attend meetings over the future of the company.
The unions will discuss a co-ordinated campaign of action at a meeting at the Irish Congress of Trade Unions headquarters today. A series of "no-fares" days were announced by the unions last July as part of its campaign against Mr Brennan's plans.
The campaign was deferred to allow talks to take place between the unions and officials in Mr Brennan's Department. However, unions pulled out of the meetings following interviews by the Minister before Christmas where he restated his plans to dismantle CIÉ and privatise bus routes.
The NBRU general secretary, Mr Liam Tobin, said the union was available for talks, but only if they were facilitated by an independent chairman. He said the Irish system had improved dramatically in recent years, despite some of the lowest operational subventions in Europe.
Meanwhile, sources last night suggested there was a possibility of joint industrial action between unions representing both CIÉ and Aer Rianta, which could cause widespread transport chaos during the Government's six-month presidency of the European Union.
This follows inconclusive talks last night between unions at Aer Rianta and the Department of Transport over plans to break up the company into three competing airport authorities.
The unions are due to meet on Friday to discuss the status of talks with the Department.
If they decide to pull out of the talks process, unions sources say it is inevitable industrial action would follow.