ASTI President Ed Byrne has said while the union and the Department of Education have agreed to keep talking in a bid to avert strike action on Thursday, a large chasm still existed between the two sides.
He was speaking following four hours of talks today between the ASTI and senior officials at the department.
Members from the union are to strike for seven days between now and December in a dispute over pay for newly-qualified teachers and payment for supervision and substitution duties.
They will also withdraw from supervision and substitution from 7 November.
Mr Byrne said very little progress had been made and described the talks as painstaking and slow.
More talks are scheduled for tomorrow and Wednesday.
Earlier, Mr Byrne said that the ASTI wanted equal pay for equal work and for all the children in the country to be treated equally.
He said: "I have to say there is a large gap between us and now we have to see if we can bridge that gap.
"We have campaigned for equal pay for equal work so we believe it's one of the fundamentals of the State, that we should have equal pay for equal work. The Government has not come out and said it believes the same."
Last Friday, the Teachers Union of Ireland said it will be issuing guidance to its members today directing that no member undertake any work normally done by ASTI colleagues.
This includes all teachers as well as school principals and deputy principals.
Meanwhile, the head of communications for IMPACT trade union has warned that if groups outside the Lansdowne Road Agreement are seen to get special deals, it will not be long before other public service unions look for better deals and the agreement will collapse.
The Lansdowne Road Agreement was negotiated to reverse pay and pension cuts for public service workers imposed since 2008. It extends the Haddington Road Agreement until 2018.
Speaking on RTÉ’s Today with Brian Dowling, Bernard Harbor said that groups such as the ASTI and the GRA have "legitimate issues" but opinions differ on how progress is made and pay can be restored.
He said that it was important for public servants and their unions to place their concerns "within the bigger picture" and that while everyone would "love to see full income recovery back to the situation we were in back in 2008", this was not possible.
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