Some 55 people are expected to lose their jobs at the end of the year when the Killeen Corrugated Products plant in Ballyfermot, west Dublin, closes.
A spokesman for Smurfit Kappa, which owns the factory, said it was hoped that around 25 of the 55 staff would be redeployed within the group.
He said high operating costs were a factor in the decision and that the plant would close at the end of the year. It is understood that a fall-off in business from key customers such as C&C group brands was also a factor.
Siptu, the union representing workers at the company, was told of the decision today and immediately sought talks on saving the jobs.
Branch organiser Pat Ward said the announcement came as a shock to the workers, who had agreed improved efficiencies and flexibilities following the loss of 53 jobs in March.
"Our bottom line is that we will do everything we can to secure as many jobs through redeployment to other Smurfit's plants in Walkinstown, Dublin, Cork and Lurgan, Co Armagh," Mr Ward said.