The owners of Bausch and Lomb have threatened to pause expansion plans in Waterford and look at other production sites.
Valent Pharmaceuticals Ireland say the recent ballot by SIPTU members for industrial action puts the future of the plant at risk.
Employees are seeking full restoration of pay cuts implemented in 2014 - and are due to begin industrial action on December 21.
Management warned the 1,250 employees in Waterford they will take further actions if the industrial action goes ahead.
This morning's statement by Valent Pharmaceuticals Ireland, trading as Bausch and Lomb Ireland, said: "This ballot follows recent rejections by SIPTU members of two carefully considered pay deals proposed by both the WRC and the Labour Court.
"The company views the new request for 'full restoration' as a challenge to the viability of the site, and as such, has set out a series of actions that would arise as a direct consequence of the industrial action scheduled to commence on the 21st of December.
"The continuation of industrial action into the New Year will lead to the consideration of further actions by the company.
"While we remain committed to the Waterford site, we will not be considering calls for 'full restoration' and a return to the uncertainty of a number of years ago. Our goal is to maintain the viability of the plant and reach a positive resolution of this matter by the 16th December.
"The company will not be making any further public comments at this point. Our primary focus is on speaking to our employees and keeping them fully informed of any new developments."
SIPTU's Allen Dillon said: "Our members have decided to implement a campaign of limited industrial action, which will consist of a series of one-hour work stoppages by each shift and an overtime ban, which will commence on 21st December.
"This dispute has arisen because of a failure by management to agree for the full restoration of the pay and conditions of employment of our members.
"In 2014, over 800 SIPTU members reluctantly agreed to deep cuts in their pay and terms and conditions of employment. The basic pay of our members was cut by 7.5% and there were additional reductions in bonus payments and sick pay benefits.
"Also, a new starter rate of pay was implemented for temporary staff and our members agreed to increase productivity by working an additional hour a week. In August 2015, an agreed two-year pay freeze expired.
The union has since been negotiating with the company in an effort to reach an agreement on full pay restoration for our members, but an agreement has not been reached.
Mr Dillon added: "A Labour Court recommendation issued in August this year in relation to the dispute was overwhelmingly rejected by our members. With the collective dispute resolution procedures exhausted and no further engagement by management on the issues in dispute, our members feel they have no option but to implement a campaign of industrial action."