Ronnie Smith, the union's general secretary, said that if employers are allowed a free rein on restructuring posts large numbers of promoted jobs in primary and secondary may never be created because of the squeeze on costs. Existing senior teachers may be the casualties.
"I say to those authorities intent on having a bonfire of promoted posts that they do need to tread carefully," Mr Smith said.
Addressing a conference on management in primary schools in Edinburgh (page four), Mr Smith condemned unnamed authorities for making a "mad dash" to radically reform management structures before August.
"In their haste, there is a risk we see some unworkable and unsustainable models and that danger arises also from their motivation. It is increasingly clear that the funding agreement between Cosla (the Convention of Local Authorities) and the Scottish Executive is creaking at the seams," he said.
"It is also clear there is a concerted attempt to claw back some of the additional costs of the agreement by creating a bonfire of promoted posts, regardless of the need for these posts."
Mr Smith said the immediate challenge for primaries was placing existing promoted staff in new posts - some 3,000 senior teachers. "It is fairly clear to me they will become substantive principal teachers, with posts subject to the job sizing process, or they will relinquish their senior teacher's post and assume the role of teacher. It is one or the other."
Some authorities were ignoring the national agreement in ruling out the PT option, by stating that senior teachers "may be eligible" to apply for posts. "Had we intended the circular to say that, it would have been formulated in exactly those terms, but it wasn't. It would have been a nonsense because anyone can apply for a promoted post.
"To compound matters, some authorities have invented a range of other options beyond the two options so clearly set out in SNCT 14 (the Scottish Negotiating Committee for Teachers document). There is no third or fourth way and what is certainly not on is the attempt to seduce some current postholders to revert to main grade teacher status while retaining their old promoted post duties."
Some authorities were desperate to flatten structures and remove grades but were now trying to plug the gap by having main grade teachers carry out the functions of existing promoted post holders.
He reminded the Murrayfield Stadium conference, organised by the Centre for Educational Leadership at Edinburgh University, that the senior teacher post in primary was subverted because of the shortage of management posts.
When structures are being drawn up for primary, they should reflect the demands on management, Mr Smith said. "The starting point should be translating those senior teachers in primary who wish to become principal teachers to that position without more ado."
Laying down a marker on the principal teacher post in primary, Mr Smith warned authorities against using PTs as a cheap alternative to depute heads. "Principal teachers do not act as headteacher substitute in secondary schools and it should not happen in primary schools," he said.