THE Teachers' Union of Ireland (TUI) is recommending rejection of the Lansdowne Road Agreement on pay in the public service.
The deal would restore around €2,000 to the pay of most public servants in three phases between January 2016 and September 2017.
But the TUI said the proposals did not allay a number of significant concerns of lecturers in institutes of technology and teachers in second-level schools.
It is calling for a No vote when its members ballot in the autumn.
Meanwhile, the Irish National Teachers' Organisation (INTO) said it favoured accepting the deal.
INTO general secretary Sheila Nunan said acceptance of the agreement was an opportunity to begin to recover income that had been lost through pay cuts and the pension levy.