Most state schools across England and Wales will have to close completely on several days in February and March if the country’s biggest teaching union votes for industrial action this week, the Observer has been told. In what would represent a dramatic escalation of the chaos sweeping the public sector, and affect millions of working parents, the National Education Union (NEU) expects a ballot of its members, which ends on Friday, to approve action that would trigger the biggest shutdown of schools for many years. The NEU’s general secretary, Kevin Courtney said action by its members alone would be enough to cause many schools to close. Other teaching unions including the NASUWT and the headteachers’ union, the NAHT, will also receive results of ballots on strike action in the next few days. The unions are understood to be coordinating strikes and strike dates. Courtney said he was confident that those who voted in the ballot would be overwhelmingly in favour of strikes, but that he could not yet be certain that the threshold for industrial action would be met. Under legislation introduced by the Tory government in 2017, union ballots must have a turnout of at least 50% and the action must have the support of at least 40% of all members, not just those who voted. For example, if turnout is 50% that means an 80% vote in support of strike action is needed. Courtney urged all NEU members who had not voted so far to do so before Friday’s deadline. An announcement of the result will be made on 16 January. “We are urging all members to use their democratic right to vote,” Courtney said. “I think we are going to pass the threshold, but there is a chance we won’t. I would urge every member who has a ballot form to return it.” In the event of a vote for industrial action, Courtney said: “We will call on members in all schools in England and Wales to strike – many would have to close.” He said the union was aware of the need not to alienate parents and believed most would understand the action teachers were taking: “I think parents are starting to pick up the day-to-day situation in schools – that their child’s maths teacher might never have acquired a maths qualification, that there is such a rapid turnover of teachers all the time, that there is a lot of disruption. “We are preparing leaflets to go to parents, getting parents to do videos. Information will be circulated via Facebook. Leaflets will be distributed at school gates. There will be lots of campaign events.” It is believed that the NEU, which has more than 450,000 members, is planning several days of action from the start of February until mid-March, in a first phase. These would involve a mix of national days of action, and days when strikes would be confined to regions. The NEU is looking for a pay rise of 12% rather than the 5% offered so far by the government for most teachers. The unions says teachers’ pay has fallen by about 24% relative to inflation since 2010. In July last year, the government said teachers would benefit from pay increases of between 5% and 8.9% from September 2022, after fully accepting the recommendations of the independent School Teachers’ Review Body for this academic year. A key factor in the dispute is how much of any increase would have to be met from existing school budgets. The government is currently refusing to offer any extra funding to cover pay rises, pushing thousands of schools across the country into deficit and forcing headteachers to contemplate sacking staff. It is understood that the NEU would be willing to talk seriously about an offer closer to 9% if this were to be “fully funded” by government. Courtney insisted that there was still time for ministers to “put money on the table” and hold meaningful talks over pay. If they did so, the strikes could be suspended while negotiations took place. In 2016, a strike by the National Union of Teachers’ – the forerunner of the NEU – left an estimated 7,000 of England’s 22,000 state schools closed or partly closed for the day. The strike was in protest at teacher workload pressures as well as pressures on funding that led some schools to lay off staff despite pupil numbers rising. After a week of chaos on the railways and with nurses planning a new wave of strikes, the prime minister, Rishi Sunak, announced on Friday that all departments had invited unions in their sectors to meetings on 9 January to discuss pay. But government sources said these meetings would concern only next year’s pay award, not the disputes over this year’s offers. Teachers in Scotland are expected to walk out this week after the latest talks with the government broke down. The Educational Institute of Scotland (EIS), which is the sister union of the NEU, the NASUWT and SSTA organisations are due to strike on 10 and 11 January after rejecting an offer that would have seen the lowest-paid members receive a 6.85% pay increase.