The moderate Association of Teachers and Lecturers joined the traditionally militant National Union of Teachers in attacking proposals linking salaries to appraisal and pupils' results.
At its Harrogate Assembly, the ATL passed an emergency motion calling on the union to defend teachers against pay linked to pupil performance and unmanageable workload. It endorsed ballots for industrial action.
This weekend the National Union of Teachers will endorse a programme of non-cooperation with performance pay and a one-day strike in the summer term at its Brighton conference.
Peter Smith, the ATL's general secretary, called on the Government to delay the timetable for introducing the appraisal arrangements which will determine whose performance deserves extra pay and access to higher pay scales.
But Education Secretary David Blunkett rejected that call, saying the money needed has already been allocated by the Treasury and must be spent before the next general election.
However, he promised to consult widely on implementing Green Paper proposals, and tried to reassure teachers that the Government was not interested in crude payment by results.
Teachers "must not constantly think of themselves as victims", he added after saying he was "mystified" as to what teachers would gain from industrial action.
"It would discredit teachers in the eyes of parents and others whose normal day-to-day work always involves some sort of assessment of their performance when they are promoted," he said.
Mr Smith said he was disappointed that Mr Blunkett had not announced a decision to reschedule appraisal.
But he suggested there were grounds for negotiation -even over performance-related pay.
The ATL general secretary could find himself at odds with his members. Delegate after delegate stood up to criticise the Green Paper, particularly the workload it will place on teachers going through the threshold, who will be expected to do extra hours and take on new responsibilities.
Before the conference, Mr Smith said that the Green Paper package could put reaching the Government's targets for pupil performance in 2002 in jeopardy.
"If the Government is determined to head for a showdown, they will alienate the very people who could deliver their electoral promises and that's a tragedy.
"In nearly 30,000 schools, either lip service will be paid to performance management or you will get the equivalent of civil disobedience and an appraisal system that's hollow, because management realise the managed are not going to take it seriously."