Head teachers in England are to hold another vote on whether to strike over pay, funding, workload and wellbeing.
The National Association of Head Teachers union (NAHT), mainly representing primary heads, had already voted overwhelmingly to reject the government's pay offer for teachers.
The union held a strike vote in January which supported taking action but did not reach the required 50% turnout.
The Department for Education said its pay offer was "fair and reasonable".
Talks between the government and the NAHT and other education unions - the NEU, ASCL and NASUWT - took place in March.
That resulted in a pay offer comprising a 4.3% rise next year, as well as a £1,000 one-off payment this year. Starting salaries would also rise to £30,000 from September.