The Pfizer pharmaceutical multinational faces strikes in the coming weeks after SIPTU members voted to back industrial action in a dispute over pensions.
SITPU members at Pfizer's Ringaskiddy plant in Co Cork will strike for 24 hours on 15 February.
They will escalate their action to a 24-hour stoppage at both Ringaskiddy and Little Island in Cork on 18 February.
The union has warned that further strikes could take place if the dispute is not resolved.
In addition, from 16 February there will be an indefinite overtime ban.
SIPTU is objecting to Pfizer's plan to change from the existing Defined Benefit pension scheme to a Defined Contribution scheme from 1 April without the agreement of staff.
The current DB scheme is non-contributory, meaning staff make no contribution towards their pension benefits - which Pfizer describes as "very unusual in either the public or private sector".
Pfizer has argued that the cost of funding the DB scheme has risen tenfold since 2009, which is affecting competitiveness.
SIPTU has resisted the proposals for change, arguing that Pfizer employees in other countries have been allowed to remain in defined benefit schemes, which are generally viewed as more secure.
Union members rejected a Labour Court recommendation aimed at resolving the dispute, and say they have now been left with no option but to take industrial action.
SIPTU Organiser Ray Mitchell said that the company was aware that the current joint union/management collective agreement remains in place until a new one is negotiated and agreed with union members.
He said that until then, there can be no alteration or amendment to the existing DB scheme.
Pfizer said it had participated in four years of negotiations through the industrial relations process - and had accepted the Labour Court recommendation which made significant improvements on the company's original proposal in 2014.
The company says that the proposed changes will affect around 900 Pfizer employees across four sites in manufacturing, shared services and commercial operations.
A further 1,400 workers who have pension benefits in Ireland are already in Defined Contribution schemes, and their arrangements will not be affected.
Pfizer also noted that the replacement of non-contributory Defined Benefit pension schemes would be for future accrual only, and that the company would continue to fund the existing schemes in accordance with its obligations.
A spokeswoman for Pfizer said the company "is disappointed that the outcome of the union ballots support industrial action, which is disproportionate".
The company has "accepted the Labour Court recommendation which includes enhanced terms and transitional arrangements", the spokeswoman said.
"Pfizer's defined benefit pension schemes provide benefit values at the upper end of the pension benefit range and the defined contribution scheme recommended by the Labour Court also provides pension benefits at the upper end of the scale," she said.
The spokeswoman added that the company "has allowed significant time over five years to work with colleagues on the changes to the defined benefit pension schemes".
"The Labour Court recommendation's proposals are very generous including lump sums of up to €35K, company contributions of up to 15% of pensionable pay, early transition incentives of up to an extra 14% of pensionable pay per annum on top of company contributions, or for those who do not transition early, 3 to 7 extra years of accrual in the defined benefit schemes based on a colleague's age at 30 June 2018 and the opportunity for colleagues over 50 on 30 June 2018 to stay in the defined benefit scheme until such time as they retire or leave the company."
The company said it would also commit to "funding what is accrued already in the defined benefit schemes" and would continue to do so at considerable cost, "so colleagues benefit from what is held in their DB pension".