Thirty seven people are to lose their jobs at the Corus Service Centre on the Ballymount Road in west Dublin. The company supplies steel to the construction industry.
SIPTU said it had been in discussion with the company on a voluntary package for 12 workers over the last few weeks, but the extra redundancies were announced sooner than the union had expected.
Corus, which is also in Lisburn and Cork, said the announcement was part of a reorganisation of its Irish activities.