Delegates at the National Union of Teachers' annual conference, instructed their leaders to ballot for a stoppage "at the earliest possible opportunity in the summer term", to win a £2,000 pay increase for all teachers, with no strings.
The decision, on the last day of the Harrogate conference, was a victory for leftwingers against Doug McAvoy, the general secretary, who pleaded for more limited action, including a work to rule in which teachers would boycott non-contractual duties such as sports coaching and school trips.
He said he would not try to thwart the will of the conference by failing to call a ballot, as union activists complained he did after losing votes in previous years. But he would refuse to obey an instruction from delegates to "campaign vigorously to ensure a positive yes vote for strike action".
Mr McAvoy said: "I am not prepared to campaign for a yes vote because to do so would be dishonest. It would imply that I support a national one-day strike and believe it would be effective." Such action would alienate parents. They would see it as an attempt by militants to let off steam without any realistic hope that the government would drop its plans. The next steps will be decided by the union's national executive, on which moderates supporting Mr McAvoy normally have a majority of 24 to 18. The outcome is likely to be a ballot during the summer term, with the executive campaigning for a work to rule and presenting teachers with the arguments for and against a one-day strike, without making a recommendation.
David Blunkett, the education and employment secretary, said: "This is the first time in history that a trade union conference has called for a strike against its members being offered promotion and extra pay simply for doing their job well."
The conference voted for a strike by 105,208 to 82,114 after a heated debate spread over three days. Delegates were united against the government's pay scheme, despite the attraction of a £2,000 performance bonus in September for most of the 240,000 experienced teachers who are currently stuck at the £24,000 maximum for classroom staff.
Mr McAvoy said the system for assessing which teachers deserved the increase was "flawed, unjust, misguided and educationally unsound". But he said the fight was a long-term struggle.
Although leaders of the other unions are going along with the scheme, a survey of NUT members showed that 60% of members wanted a one-day national stoppage.
John Lockwood, of the union's mid-Warwickshire branch, said: "There is not a teacher in the land who does not know the £2,000 is a bribe offered to break our conditions of service."
Liz Rattue, an Islington teacher, said: "If we want to protect our members from being catapulted back to Victorian times, we must embark on a serious programme of industrial action and do it now."
In a speech to the conference before the result of the strike motion was declared, Mr McAvoy said: "The friendship and teamwork of teachers - the very glue that holds schools together - will be blown apart by this pay system."
He later questioned the legitimacy of the conference decision. The first vote on an amendment to include a one-day stoppage in the main motion was passed by a majority of 5,000, thanks to the block votes of big delegations. But there were more individual delegates voting against a strike than voting for.
"The amendment was carried by the smallest of majorities, not because of the arguments and the facts used in the debate, but because of the pre-determined political posturing of some delegates," Mr McAvoy complained.
