The result of the ASTI national ballot on a Government offer of €38-per-hour for supervision duties will be known late this afternoon at the earliest.
The result of the ballot, which attracted a turnout of over 50 per cent of the union's 17,000-strong membership, is expected to be very close.
The union's leadership had urged secondary teachers to reject the Government offer, despite the fact that the deal has already been accepted by the other teaching unions.
Last year, ASTI members endorsed the supervision deal by 63 per cent to 37 per cent. The turnout was 55 per cent. A re-ballot was called by the ASTI leadership because of a dispute about payment for "on-call" working.
Until the ASTI dispute, teachers performed supervision-and-substitution duties on a voluntary basis.
The Minister for Education, Mr Dempsey, has warned he is poised to impose new supervision arrangements for schools if the current offer is rejected.