Thousands of teachers in the UK have voted to strike over changes to their pensions and pay.
The NASUWT union said 80% of those who voted backed the action, but added it was "not inevitable" that its members would strike on 30 November with other public sector workers.
It has announced its members will work to rule from 1 December.
But other teaching unions are poised to join the national day of action and thousands of schools could close.
The NASUWT balloted more than 230,000 members in England and Wales, Scotland and Northern Ireland.
It asked members if they were prepared to strike and also if they were in favour of action "short of a strike".
With a turnout of about 40%, it says 82% voted for a strike, while 91% backed action short of a strike.
Its leader Chris Keates said she hoped there will be movement from the government and that the main focus would now be action short of a strike - in effect, a work to rule.
"There is nothing inevitable about 30 November, it's a last resort, " she said.
"It is not the main focus. The members of the NASUWT have voted for industrial action that will be pupil, parent and public friendly.
"The coalition government needs now to take seriously the concerns voiced by the teachers today.
"This is a vote that cannot be ignored."
The union has said regardless of what action is taken on 30 November, its members will take industrial action short of a strike from 1 December.
This could mean teachers not working more than 32 and a half hours a week and refusing to carry out administrative tasks such as collecting money, putting up displays and administering exams.
Teachers and heads are angered by planned government changes to the teachers' pension scheme (TPS) which, they say, will mean teachers working longer, paying more and receiving less when they retire.
The government says with people living longer, the cost of public sector pensions is rising and reforms are needed.
Earlier this month it made a new offer, including protection for anyone within 10 years of their pension age.
Negotiations are continuing between it and the unions.
Schools Minister Nick Gibb said: "Strikes benefit no one. They damage pupils' education, disrupt parents' lives, and undermine teachers' professional reputation.
"The Teachers' Pension Scheme will remain one of the best available and fair to taxpayers and teachers. The current offer means teachers will continue to receive a pension that is better than anything offered to most private sector staff."
He added: "News that NASUWT is planning to work to rule will worry parents, pupils and their families. That could mean huge disruption to school plays, sports and everything else schools do to enrich their pupils' lives."
The NASUWT has lodged a formal trade dispute with the government over workload, conditions of service, pensions and jobs.
Mr Gibb said the government had put in place reforms to reduce bureaucracy in schools and free up teachers to teach.
The government has been giving schools advice on how they might stay open in the event of a strike and cover for absent teachers.
Schools will be taking decisions soon on whether to stay open on 30 November and will begin telling parents.
Under union law, union executives need to give notice that they are taking strike action at least seven days before action is taken although individuals do not have to tell their employer they intend to strike.
The National Union of Teachers and the Association of Teachers and Lecturers have already voted for strike action over pensions, as has the National Association of Head Teachers - in the first strike call in its history.
The NAHT has not yet said it will call a strike however and is hoping for movement from the government.
Unison, which represents many teaching assistants and other school support staff, on Friday said it had sent out letters telling employers of its intention to strike on 30 November over pensions.