Jimmy Docherty, the union's assistant secretary, said members in 20 secondaries had complained that heads were acting precipitately in trying to impose their view about the allocation of collegiate time in teachers' contractual 35-hour week.
Such actions were breaking the spirit of co-operation behind the post-McCrone deal, Mr Docherty said. "There is a total, complete failure by certain headteachers to adopt a participative management style. The term Victorian mill owner has been reported to me on more than one occasion."
He added: "It has to be made clear to headteachers that they are living in a completely new era. They have to sit down with members of staff and then come to some form of agreement and some agreements will send shivers down the spine of certain headteachers. Their skills are going to be tested and it will be beyond some."
Mr Docherty also questioned the ability of some authorities, particularly smaller ones without experienced education personnel, to deal effectiely with the negotiations.
Ronnie Smith, Educational Institute of Scotland general secretary, said: "This is about changing mindsets and the climate and culture that has grown up since the 1980s. The big shift is that an awful lot of matters will have to be sorted out at school level and that is very different.
"Heads will be involved in a process they have hitherto not had to do. And our reps will have more responsibility on a whole number of matters previously decided by other people in other places."
Mr Smith said schools would have to recognise that the extra time within the 35 hours was limited. "We are talking about flexibility, not open season. It's not a requirement to have endless amounts of work for teachers."
Cutting workload was a key ingredient in the agreement and schools would have to narrow their ambitions. Some aspects of forward planning, for example, may have to go. "There is a limited pot of time available. Schools will have to ask whether previous priorities are sustainable in the new environment."
Agreements should be in place before the summer break. Teachers receive a 10 per cent first-stage pay hike later this month.