The Association of Secondary Teachers has told its members the Leaving Cert proposal cannot be enforced.
The State exam has been pushed back from its traditional start date at the beginning of June, to either late July or early August.
A statement on the union's website says "no teacher will be required to do anything." and says the proposal on the state exams "cannot be enforced".
The ASTI says it has a number of concerns and needs clarification from the Department of Education, around several points.
ASTI spokesperson, Kieran Christie, says the union does have a number of concerns they are raising with the Department of Education.
"There remain aspects and practicalities that we need clarification on," he said, citing the revised deadlines for project work, practical work and the needs of special education students.
However, Seamus Lahart, President of the Teachers Union of Ireland, says he will be asking his members to help students prepare for the exams.
"We have considered the Minister's request - particularly that we engage with students for two weeks during the month of July - and we are asking members to engage in the process as a whole-school response to meet the needs of our students.
"I am proud of teachers so far in the efforts they have made in extraordinary circumstances," he added.