The Teachers' Union of Ireland has expressed concern at the potential impact of a Government proposal to limit the number of Junior Certificate exam subjects to eight for next year's first year students.
The TUI said the decision has caused consternation among teachers and principals, who say it could cause chaos in schools.
The union said it could lead to a drop in student motivation and an increase in indiscipline in schools.
Under the proposal, students commencing second level in 2012 will only take eight subjects to examination level.
The Department of Education said this is to address subject 'overcrowding' and to free up more time to concentrate on core skills, such as literacy and numeracy.
However, the TUI said many classes could end up with a mix of students, some of whom are taking an examination and others who are not.
It said this will lead to clear de-motivation and discipline problems in the classroom.
The union said this will be greatly exacerbated in schools that have already been badly hit by a range of cutbacks.
The union also said many schools will be forced to drop subjects such as art, history, geography, technology and music as examination subjects.