The Association of School and College Leaders is to formally ballot its members for strike action – for the first time in its history – in an escalation of the dispute over teachers' pay and school funding.
The vote will take place during the summer term and if enough members vote yes, strike action would likely take place in the autumn.
ASCL has around 23,000 members at all levels of school leadership and who predominantly work in secondary and further education.
The union is in dispute with the government over the school funding crisis, the erosion of teacher and leadership pay and conditions, and consequent staff shortages which it says are undermining the education system.