Business group ISME is blaming inter-union rivalry for next week's planned work stoppage at CIE.
SIPTU says its members will stop work for 24 hours on the day after Saint Patrick's Day, saying talks with the Government on the future of CIE are not productive.
However, the union representing most bus drivers, the NBRU, is not planning to follow suit at this stage.
Chaos is still looming as many NBRU members may refuse to cross the SIPTU pickets. Mark Fielding, of ISME, says it is a case of a smaller union playing hardball to assert itself.