Dublin Bus drivers are warning of industrial action over a ban on them listening to the radio while on duty.
The new rule came into force yesterday and the National Bus and Rail Worker's Union says its members will be balloted on Thursday.
The union says one of the main points of concern is health and safety in the Port Tunnel where all drivers must have a radio turned on so that emergency services can interrupt the transmission in case of emergency.
General Secretary Dermot O'Leary says his members don't want to strike but drivers shouldn't be punished.
"We've just been informed today that a number of our drivers have had disciplinary measure recorded against them.
"What our members are saying quite clearly is that if ultimately sanction was to accrue to a driver as a result of this - they are acting on Union advice - then obviously the mandate we are seeking for industrial action - then industrial action will take place."