The ASTI insists it wants to have a legal stand-off with the Department of Education resolved as soon as possible.
It's advised it's members not to engage with the new calculated grades system for Leaving Cert students.
Guidelines were issued yesterday which protects teachers from getting undue influence from students while attempting to give a predictive mark.
Students can be reported to the Department of Education.
The union says its legal advice has warned them that teachers costs won't be 100 per cent covered if they are sued.
President of the ASTI, Deirdre Mac Donald, says they want the Department to offer further reassurance;
"We employ lawyers and they tell us that this has the potential to leave our members to a possibility of the third of the cost, now we're just not going to lay our members open to that."
She went on to say;
"We want this sorted, we actually made it very very clear to the Department of Education and the Attorney General's office, whose the one who is writing the indemnity."