Teachers in England will vote on whether or not to go on strike if the government stands by its pay offer for the next school year.
The National Education Union (NEU), England's largest teaching union, says it will hold a formal ballot if the offer remains "unacceptable", or if no extra funding is announced.
The government has recommended a 2.8% pay rise for teachers and expects most schools will need to make "efficiencies" to fund it.
Education Secretary Bridget Phillipson said "any move towards industrial action by teaching unions would be indefensible".
The NEU wants a higher pay rise for teachers, and for the government to announce more money so that schools do not have to pay for it from their existing budgets.
The announcement from its conference in Harrogate is a warning to ministers, but a few things would still need to happen in order for teachers to walk out of England's schools.
The union will need to reject a final decision from the government on teacher pay – including both the size of the pay rise, and whether or not there will be any additional funding for it.
If it does launch a formal ballot, enough members would need to vote and support strike action. That ballot could open for several months, meaning any strike action would likely take place in the autumn term at the earliest.
