ASTI delegates have rejected one of the main features of the £67.7 million Government offer on pay and conditions - promotion on merit - before conference considers the offer this morning.
Delegates voted yesterday to resist changes in the procedures to fill posts of responsibility in second level schools.
The conference overwhelmingly supported promotion on seniority, even though an internal union survey showed it was the least favoured option among members.
The Government package proposes that posts of responsibility should be filled on the basis of merit, a procedure already in place in vocational and community schools.
Mr Pat Younger, New Ross, said the ending of seniority was responsible for the rejection of the package by ASTI members.
Present arrangements endured there was no "bickering" between staff members over the filling of posts.
"It also ensures that the ethos of co operation between teachers for the well being of the whole school is not replaced by an atmosphere of mistrust and favouritism which could damage the school and staff," he said.
If teachers were qualified to teach, then they were qualified to perform the duties of any post.
Changes could lead to victimisation by the principal and an auctioning system for appointments whereby the person who is "seen" to do a lot is successful.
Mr Younger said promotion on merit would result in further discrimination against women, political appointments and excessive power for the trustees.
The survey of more than 800 ASTI members showed only one teacher in five preferred seniority as the criterion for appointment of postholder.
Open competition was favoured by one quarter but tile most popular option, preferred by more than half the respondents, was a combination of open competition and seniority.
Large numbers of teachers criticised the system in for failing to provide a career structure or to divide school responsibilities.
But it was praised for helping to avoid conflicts over appointments.
Opposing the motion, Mr Paul Thornton, Donegal, said that in an era of falling enrolments, it was unrealistic for junior teachers to be given the expectation they would obtain a post.
Ms Patricia Wroe, Dublin South County, argued that "schools are not about production; they're about collegiality and working together. `Dog eat dog' and `I'll get you' is not what we are about," she said.
Have young teachers become so disillusioned with their vocation that they want to get involved in internal management, asked Ms Bernadine O'Sullivan, Dublin South West.
"The most important task in schools is teaching. That is what we as a profession are qualified to do.
"The present system is open, transparent and fair, just like the points system we recommend to our students."