Teachers' unions have threatened strikes in the autumn against 'attacks' on jobs, pensions, workload and pay. Photograph: Owen Humphreys/PA Schools in England and Wales face the threat of strike action in the autumn after the two largest teaching unions – representing 600,000 teachers – announced an "unprecedented" joint protest over the government's education policies. The NUT and NASUWT, who between them represent nine out of 10 teachers in England and Wales, have called on the education secretary, Michael Gove, to hold joint talks with their general secretaries or face walkouts by more than 600,000 education professionals after the summer. Alluding to historic tensions between the unions, the NUT's general secretary, Christine Blower, said the government had succeeded in bringing together the UK's two largest teaching organisations in a "historic" agreement. "Michael Gove has managed to get us to a point where we are making a joint declaration," she said. She added: "We would say this is quite unprecedented and historic. This is the first time that we have actually put anything out which categorically bears the emblem 'joint declaration of intent'. This is qualitatively different from what these unions have done before." However, the NASUWT's general secretary, Chris Keates, said a merger between the unions was not imminent. "At the moment the focus has to be on the savage attacks by the government. Our priority at this time is protecting teachers in the profession." In a joint statement, the unions criticised "sustained attacks on working conditions, pensions, pay, conditions of service and the threat to jobs". Both unions took part in the 30 November public sector strikes over pensions reforms. The unions said if the government failed to reach "sensible agreements which protect teachers and defend education" then they would move to jointly co-ordinated strikes in the autumn. The campaign would include joint work on political lobbying, public campaigns and research. Both general secretaries accused the government of undermining teachers through pension reforms, a two-year pay freeze and its flagship free schools policy. "In the commercial world if you are the chief executive of a company you don't improve things by constantly talking down the people you employ," said Blower, whose union will seek a fresh ballot to widen the terms of its industrial mandate. However, recent signals from Gove's department do not augur well for the NUT and NASUWT. A leaked briefing from Gove's chief strategist, Dominic Cummings, lambasts the unions for their "refusal to face reality over grade inflation and the dumbing down of exams". Keates said the concessions being sought by the unions were, essentially, a request for the government to cease its reform drive. "We are actually saying 'leave well alone'. The pay and conditions structure [was] paying real dividends in raising standards in schools." Keates said strike plans had not been formalised and the unions' industrial strategy – also dependent on an NUT ballot – would be determined by the government's response to its ultimatum. "What we don't want to do is be upfront, setting out our timetable for strike action … What form strike action will take depends on the response from the government." In a statement issued by the Conservative party, the Conservative MP for south Staffordshire, Gavin Williamson, accused the unions of putting pupils' interests second. "Parents will be concerned at the threat of further strike action, particularly with a pension deal on offer that those of them who work in the private sector could only dream of. "And they will rightly wonder why these union leaders are placing their own vested interests above the interests of the young people our education system is supposed to serve," he said.