Voting by ASTI secondary teachers on the Government's €34-an-hour offer for supervision and substitution cover begins today.
At the moment, teachers are not paid for these duties and do them voluntarily.
ASTI is recommending its members vote against the offer, despite the Government’s position that it will not enter into more negotiations.
Talks on supervision were set up after the Labour Court issued a recommendation during the ASTI dispute last year, saying it was an area worth examining.
Minister for Education Mr Michael Woods has promised a review at the end of the year if the teachers accept the pay offer.
The union is expected to have a result from its ballot on January 29th.
A decision on the issuing of a directive on withdrawal from voluntary supervision and substitution has been deferred pending the outcome of the ballot.