The Irish Federation of University Teachers has become the third union in the education sector to reject the Croke Park deal on public service pay and reform.
In a ballot result announced this afternoon, the union's members opposed the Croke Park proposals by around a two to one majority.
Just under 40 per cent of IFUT's 2,055 members took part in the ballot.
A total of 32.32 per cent accepted the Croke Park deal while 67.68 rejected the proposals.
The general secretary of IFUT Mike Jennings said he was delighted at such a strong endorsement of the position of the union's executive on the Croke Park deal.
He said that it provided a strong mandate for the union to defend members' conditions and academic status.
Mr Jennings said that IFUT would not be bound by the outcome of a majority vote on the Croke Park deal when it is considered by the Public Services Committee of the Irish Congress of Trade Union next month.
Last Friday members of two other teaching unions, the ASTI and the TUI voted to reject the Croke Park deal while members of the INTO accepted the agreement in a ballot.