The General Secretary of the ASTI John White has said the public sector pay agreement is "the best deal possible".
The agreement, which will see public sector reform in return for the promise of no more pay cuts until 2014, has already come under fire from unions, with the TUI recommending its rejection.
The Standing Committee of the ASTI also said it is opposed to the deal which will be discussed in detail at its annual conference next week.
But Mr White has said he acknowledges teachers are worried about the increasing work-load.