The Association of Secondary Teachers in Ireland is to recommend that members should reject the clarified Haddington Road proposals in a ballot.
The move came following a five hour meeting in Dublin.
The 180 strong central executive committee decided that the proposals should be put to a members' vote.
It said it was not prepared to recommend acceptance.
The ASTI remains the only public service union to reject the Haddington Road agreement.
Earlier, as delegates arrived they were met by around 20 union members with placards who strongly object to another vote taking place.
They say members have already rejected Haddington Road twice and nothing has changed to merit another vote.
Meanwhile, a Department of Education spokesperson said the union has a decision to make. "We await that decision and will consider its implications."