Security officers at the Shell gas terminal in Mayo have started industrial action today in a row over changes to their working hours.
Siptu says their members have been forced into the strike due to the security firm, Senaca, laying off staff without their agreement.
The 12-hour work stoppage got underway at 6am and will continue until 6pm this evening.
Siptu Organiser Ed Kenny said: "This action has been necessary due to the company terminating Siptu members' employment without agreement and its unilateral reductions of workers' contractual hours.
"Workers have been left with no option but to conduct this industrial action due to the intransigence shown by the management in this dispute."