A union at Cadbury is seeking a guarantee that the 1,200 jobs at the Irish plants are secure after a US food giant made a successful bid for the chocolate maker.
Unite Regional Secretary Jimmy Kelly said the union was seeking urgent meetings with senior management at Cadbury and its new owner, Kraft Foods.
He said the loss of Cadbury's independence was a "very sad day" for Irish manufacturing.
The union said it was concerned about the €13bn bid because workers were excluded from takeover talks and had very little detail on the buyer's intentions.
Cadbury has manufactured in Ireland for more than 75 years and employs over 1,200 workers at plants in Dublin and Kerry.
European co-ordinator for Unite, Jimmy Whelan, said Kraft had ratcheted up its debt to purchase the company and this could mean jobs being axed.