The ASTI insists it wants to have a legal stand-off with the Department of Education resolved as soon as possible.
It's advised its members not to engage with the new calculated grades system for Leaving Cert students.
The union says its legal advisers have warned them teachers costs won't be 100 per cent covered if they're sued.
President of the ASTI, Deirdre MacDonald, says it wants the department to offer further reassurance.
