Speed camera operators who are members of the trade union Siptu are to stage another strike on Thursday.
The staff concerned will also hold a protest at Leinster House.
The dispute is over working conditions and trade union recognition.
The company that operates the speed camera van system, Go Safe, said the bulk of its services would be running despite the strike.
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Go Safe said on Thursday: “We have moved to ensure disruption caused by today’s strike action is minimised, with up to 80 per cent of roadside safety cameras in operation.”