Scottish teachers in the EIS union will begin voting this week on a deal on pay, jobs and conditions.
Rank and file teachers are campaigning to reject the deal after the union leadership did a U-turn and said it would accept minor concessions.
The deal would leave teachers with a two-year pay freeze, and supply teachers would face even lower wages and less regular work. It allows councils to cut 900 teachers.
Many local associations including the biggest, Glasgow, have voted to reject.
Schools are also holding branch meetings and passing motions of no confidence in the union leadership.