Workload an issue on GCSE reforms.
Former chief inspector of schools Mike Tomlinson is heading a review of education for 14-16 year-olds and is expected to publish his final report within the next fortnight.
One proposal is reported to be that most GCSEs would be replaced with an exam which teachers mark themselves.
The Tomlinson report would recommend that teachers are trained as chartered examiners to oversee internal assessment in schools.
But teachers are worried that moving away from external exams could put greater pressure on staff.
Headteachers and business leaders in the North gave Mr Tomlinson's interim recommendations a broad welcome.
It is thought that his final report will recommend a move towards a diploma-style system to replace A-levels and GCSEs.
But John Bangs, from the National Union of Teachers, said: "There is a big question mark over work-load and teachers are very weary of change.
"Unless there's a fundamental understanding that there's time available for proper, structured teacher assessment, then what is otherwise a very good proposal is going to get knocked back."
David Hart, general secretary of the Secondary Heads Association, said using IT for internal assessment would help keep workloads manageable for teachers.