Secondary school teachers are threatening to stop supervising pupils in a row over pay.
Their union, the ASTI, says their colleagues hired after 2010 are being paid less for the same work.
Staff have also warned that they will not offer substitute teachers until the row is resolved.
Members are to be balloted on industrial action.
However, ASTI general Secretary Kieran Christie says the union will continue to discuss the issues with the Department of Education.
He said: "Well the Minister has stated the belief that continuing dialogue between the ASTI and his department was in the best interest for everyone and this is a point on which we would totally agree.
"We will continue to engage with the department constructively with a view to resolving all these issues."