If approved, it could lead to the "unacceptable endorsement of a situation where teachers are expected to deliver areas of the curriculum in which they have no specific qualifications," the GTCsays.
Over the years, the GTC has refused to accept any watering down of the direct link between teachers' qualifications and subject departments. This stance effectively vetoes Glasgow's scheme for a new category of teacher.
In its consultation paper Teaching in Glasgow: high status and high standards, the city calls for general studies teachers to cover for short and long-term absences.
These teachers would be new recruits to the profession employed full-time at specific schools where they would be familiar with the pupils and procedures.
The city argues that pupils would benefit by not having a series of temporary staff. The new staff could also work co-operatively in their own subject area, help in the alternatives to exclusion projects or provide extra assistance in support for learning.
But the GTC says general studies teachers would be a "contradiction" in the Scottish secondary school and a "dangerous departure from the subject specific basis of secondary education, which is one of the undoubted strengths of the Scottish system".
The council can "point with no little pride to the high degree of match in secondary schools between subjects taught and qualifications held".