Jim Docherty, the union's assistant secretary said: "This is not a better standard of education for pupils. We totally oppose the Glasgow proposals which go well beyond what the vast majority of local authorities are proposing."
Mr Docherty, responding to last week's TES Scotland report on the city's alternative approach, added: "Once you get beyond first-line guidance to matters such as parental or agency contact or extended pupil interviews, then this should be done by trained guidance staff and not, as Glasgow is proposing, that all teachers should deal with this level of problem."
In a thinly disguised attack on the Educational Institute of Scotland, he continued: "Why has this been accepted by the union side? The SSTA dissents."
The union argues that the post-McCrone national agreement made no changes to teachers' pastoral duties and that any suggestion class teachers would have had to do the work of promoted guidance staff on top of their other duties would have been rejected.
Plans to call staff "student tutors" and ask them to deliver first-line guidance were dismissed as a "sleight of hand".
Mr Docherty said: "This implies that student tutors and teachers are one and the same when patently they are not and should not be. Student tutors should be trained, promoted guidance staff."
He called on Glasgow to seek extra resources to protect the number of promoted posts and train staff. "Teachers will not and cannot be trained guidance teachers by August," he said.
He further attacked suggestions that secondary teachers would be following the model of colleagues in primary. "This is simply the wrong way round.
Primary schools should have promoted guidance staff like secondaries," Mr Docherty said.