Industrial action will get underway later today at the Bausch and Lomb plant in Waterford city.
SIPTU members will hold a two-hour work stoppage from midday at its manufacturing facility, in anger over their pay.
The union claims management has failed to give them enough of a pay rise as workers struggle with the cost of living crisis.
SIPTU Sectoral Organiser Neil McGowan says the offer so far from the company isn't adequate.
