Strikes at Bus Éireann and Dublin Bus next month could cost the companies up to €5m.
Bus Éireann says it is a huge loss and wants more talks to try and hammer out a solution.
The National Bus and Railworkers Union (NBRU) yesterday announced a combined total of
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SIPTU drivers are to strike for four days.
NBRU general secretary Dermot O'Leary wants action from the Minister for Transport Paschal Donohoe after his call yesterday for the strike to be called off.
"I suppose the minister has been out certainly yesterday and again last week talking the talk - and I suppose it's time now for the minister to transfer that talk into some type of action," he said.
"Pontificating and commentating is something that this Government and Minister of this Government have become experts at."