The Mandate trade union has said it will be advising its members to vote No in the forthcoming referendum on the proposed EU Fiscal Treaty.
Mandate, which is holding its biennial conference in Wexford, represents over 45,000 workers mainly in the retail trade.
During his address, Mandate General Secretary John Douglas said that, if passed, the Fiscal Treaty would not create one job.
Mr Douglas said that on the contrary it will legally lock down Irish economic activity at its current levels, and may even shrink domestic demand further.
Minister for Social Protection Joan Burton described the position taken by Mandate on the treaty as ''disappointing''.
''The national debate on the Stability Treaty is only now getting under way, and it would have been preferable to have a discussion on the pros and cons of this treaty before taking a position,'' she said.
The move came amid reports ICTU may urge union members to vote Yes because of the negative fallout a No vote could produce.