Teachers, doctors and nurses are not happy with the pay deal being offered by the Government in October's budget.
Up to 60,000 public servants hired after 2011 on lower pay are set to receive more than €3,000 each under new budget proposals.
The Association of Secondary Teachers Ireland (ASTI) have said the cash offer does not resolve pay inequality issues.
The Finance Minister Paschal Donohoe is likely to sign off on the deal worth €200m this week, but the founder of advocacy group the Hibernia Forum, Eamon Delaney, has said he is not surprised by the union's reaction.
Mr Delaney said: "I wasn't surprised to see the names of the unions, the ASTI, who are just a byword in militancy on so many issues.
"The nurses' union as well, who are pretty tough, pretty demanding, I know there is difficulty with filling vacancies and with conditions.
"It's like we are back again to the Bertie era, boom to bust, if I have it I'll spend it, and the Government is spending it."