Members of the Technical Engineering and Electrical Union employed at Bausch & Lomb have voted to accept the company's proposals to retain the plant in Waterford.
68 member voted in favour, with 23 votes against.
Commenting on the outcome of the vote, TEEU regional secretary Paddy Kavanagh, who is based in Waterford, said: "The cuts to pay and conditions arising from these proposals are particularly harsh and will impact greatly on the workers affected.
"However, the alternative is unthinkable."
He went on to say: "All eyes are on the company now, to ensure that they live up to their side of the bargain and that the promised investment will proceed, thereby ensuring the future viability of the plant.
"TEEU members are committed to working with the company to ensure the plant's sustainability in Waterford and trust the company will honour its commitment to no further pay cuts."
Yesterday, more than 800 SIPTU members voted in favour of the proposals, which include pay cuts and 200 redundancies.
The contact-lens maker welcomed the outcome of the ballot, saying its preference was to keep the plant open.