Teachers in hundreds of schools with low exam results could take strike action in protest at the Government's National Challenge plan.
A high-profile campaign, including the threat of industrial action, is needed against the initiative aimed at schools where fewer than 30 per cent of GCSE pupils achieve five good grades, including English and maths, the NASUWT said.
Teachers working in difficult circumstances have been put under "intolerable" pressure by the strategy, launched by the Schools Secretary last year, the union's annual conference in Bournemouth heard.
Sue Jones, from Derby, said that the time had come to stand up against the "ludicrous initiative".
"This constant monitoring of teachers shows a lack of trust and the need for senior leadership teams to develop a culture of harassment and threatening behaviour," she said.
"All teachers in National Challenge schools are fearful for their jobs."
The conference unanimously passed a motion to implement industrial action, including strikes, where teachers are willing to participate in defiance against "the detrimental impact of the National Challenge".
It also agreed to conduct a high-profile campaign against the scheme and to challenge the Government to deny that it was designed to force more schools to become academies or trusts.
Andrew Westgarth, from north Tyneside, said teachers were having to persuade parents at feeder primary schools, concerned by negative publicity, to send their children to national challenge schools.
"The feeling of constant scrutiny coupled with the threat of job losses and school closures mean that teachers are feeling an incredible amount of strain," he said.
Ron Clooney, a teacher at a Challenge school in Southampton, described the scheme as "crap" and "nonsense".
Chris Keates, the union's general secretary, said: "Whatever the intention, National Challenge is now associated with a focus on failure and closure. In some schools, it has degenerated into a debilitating, distracting wrangle about whether the school should become an academy or trust."
Meanwhile, further threats of strike action were made by the NUT over sixth-form and college funding shortfalls. There is an estimated gap of Pounds 200 million for the next academic year because funding has not risen in line with growth in student demand. The NUT backed a motion condemning the cuts, claiming they would lead to a "rationing of educational opportunities for young people".
The union agreed to ballot for industrial action if teachers are threatened with losing their jobs as a result of the funding shortfall.