The ASTI is facing a grassroots revolt after new figures indicate that eight branches have backed motions expressing no confidence in the leadership.
The move comes amid increasing signs that the outcome of a ballot by TUI members on the Government's £27 per hour supervision offer is too close to call.
If the TUI rejects the offer when the result is made known later today it will be seen as a boost for hardliners in the ASTI.
In all, eight of ASTI's 56 branches have backed motions critical of the general secretary, the president, the central executive committee and the standing committee.
The ASTI negotiating team which emerged with the current £27 per hour offer for supervision/substitution has also been censured.
One ASTI member said yesterday the motions reflected widespread dissatisfaction with general secretary Mr Charlie Lennon and the entire leadership.
But another source said these motions were a "rearguard action by militants who can no longer run the agenda".
The motions have been sent to ASTI head office in response to what is now widely seen as a disastrous pay campaign for a 30 per cent increase.
They come from branches all over the State including those in Kerry, Waterford, Laois, Fingal, Dublin South and D·n Laoghaire.
However, four other branches refused to adopt motions of no confidence in the leadership.
In another development, a high-profile ASTI figure, Mr Bernard Lynch, is expected to begin High Court proceedings today, seeking reinstatement to the powerful 23-member standing committee.
Mr Lynch, a strong critic of the leadership, has been excluded from the standing committee after one recent meeting had to be abandoned.
Those in the TUI who support the Department of Education's £27 an hour for supervision were struggling yesterday to gain sufficient support.
But the result could still swing either way. Sources in the union said information given by the No side was proving very effective.
The union leadership is worried that if members vote No it could lead to school closures, even though some members do not necessarily want this.
A No vote by the TUI would give a fillip to hardliners in the ASTI at a time when the union appears poised to adopt a more moderate stance.
The result of a school-by-school survey now under way is expected to show strong opposition to widescale industrial action. In the TUI ballot, the No advocates insist that the Government will improve on the offer if it is rejected.
They say the Government will make the payment - worth a total of £1,000 per year to most teachers - pensionable. They also maintain the £27 per hour offer can be improved. The Yes camp insist that the current offer is the best available.
This week, the Department of Education told the ASTI that no improvement was available.
The Department of Finance is adamant that the supervision offer, which will cost the Exchequer £40 million per year, should not be increased.