Siptu staff have placed a picket at the Brinks Allied depot at Clonshaugh in Dublin as they began industrial action this morning in a row over new work practices.
They commenced the picket at 6.30 a.m.
The strike is likely to increase disruption to services provided by Brinks in Dublin and elsewhere in the east, as supervisors who have been carrying out deliveries will not pass pickets.
Drivers have been off the road since the end of last month, when the company attempted to introduce new vehicles and security procedures. The company had instructed cash delivery staff operating new delivery vehicles to drive away from a robbery scene, even if that meant leaving a colleague behind.
The row initially resulted in the closure of large numbers of non-branch ATMs in the affected east coast areas as they began to run out of cash.
However, the Irish Payments Services Organisation insists that more than 90 per cent of all machines, including those at bank branches and in retail outlets, have been operating.
Siptu said its members had been left with no option after Brinks Allied turned down a Labour Court recommendation which they had accepted.
Security branch secretary Mr Kevin McMahon said: "The strike will proceed in the absence of the employer allowing our members to return to work in the line with the Labour Court recommendation. We have been left with no alternative."
Mr McMahon told ireland.comthe union had also requested the early intervention of the National Implementation Body because Brinks was not complying with the stability and peace proposals of the Sustaining Progress partnership agreement.
The Labour Court recommended Siptu staff return to work using the new Dutch cash-in-transit vehicles for an interim period of one month.
It said Brinks Allied should also defer its insistence that drivers leave the scene of an armed robbery, even if a colleague was left behind.
Siptu made a last-minute plea to Brinks Allied last night to accept the court's recommendation.
Around 80 drivers are prepared to mount pickets, as well as 20 administrative staff in Brinks Allied. Mr McMahon said there was concern the company's real agenda was to use the dispute to close its Irish business. The company could not be contacted for comment.
Additional reporting: PA