The Technical Engineering and Electrical Union has become the third union to reject the proposed extension to Croke Park public service pay agreement.
The TEEU represents around 1,500 craft workers in the public service.
Up to 65.6% of its members rejected the deal, with 34.4% voting in favour.
Earlier, Minister for Public Expenditure and Reform Brendan Howlin ruled out further negotiations on the new proposals.
Mr Howlin said he did not want to give any false indication to anyone that there was time to have another round of negotiations.
He said they had had those negotiations and those that had involved themselves had done a good deal for their members.
However, Mr Howlin stated that those that had not involved themselves and had absented themselves would have to reflect upon their involvement to date.
Minister Howlin noted that the proposals would begin to deliver savings from 1 July of this year.
He said that it was the best deal that would achieve the target savings of €300m this year and €1bn over three years.
Minister Howlin said he was not contemplating the proposals being defeated, but would let union members make up their own minds.
Mr Howlin was reacting to comments from the Unite union yesterday on the consequences of a "No" vote.
He said it would be a Government decision on whether there would be across the board wage cuts or cuts to frontline services.
Mr Howlin rejected comments made by INMO chief executive Liam Doran yesterday.
He said it was a difficult ask for people to take cuts, but no one could be immune from it either.
Elsewhere, Sinn Féin leader Gerry Adams said it is obvious that the Government has torn up the Croke Park Agreement.
Speaking on RTÉ's Today with Pat Kenny , Mr Adams said the Government is targeting people on lower and middle incomes, and people working in frontline services.
He pointed out that Taoiseach Enda Kenny is paid €16,500 a month, which is almost as much as a graduate nurse in expected to live on for a year.
Mr Adams said it was also telling that the Government had broken the cap on its own special advisors.