The National Union of Teachers is to ballot its members to see if they are ready to strike over the abolition of management allowances for senior staff.
It is the opening shot in a war between the union and heads over plans to replace the allowances with teaching and learning responsibility points (TLRs).
The NASUWT, which supports the changes, is threatening strike action in schools where it believes heads have treated its members unfairly. It has announced plans to hold a ballot at Noel-Baker school in Derby.
The reforms aim to shift senior staff away from pastoral and administrative duties and towards raising standards.
The Secondary Heads Association said it expects legal action from staff in London who are angry at losing the allowances, at present worth Pounds 1,163-pound;10,572 per year. It said schools have little to fear if they follow official guidelines and keep the Government and local authorities informed of any concerns about missing the December deadline.
The dispute comes as the School Teachers' Review Body is due to recommend a two-year real-terms pay freeze with an annual rise close to the rate of inflation, now 2.7 per cent.
The change from management allowances to TLRs was agreed between the Government and unions that signed up to workforce reform - the NASUWT, Association of Teachers and Lecturers and SHA.
Schools in England must review their staffing structure by the end of next month, but teachers will have their existing allowances protected for three years. Thousands of staff who now hold positions such as head of year could lose out.
The NUT ballot asks members whether they are "prepared to take action up to and including strike action". It would not give the union the right to call a strike, but is designed to show the strength of feeling among staff. A strike ballot would have to be conducted by the Electoral Reform Society.
The NASUWT will ballot members at Noel-Baker school over plans to cut 40 management allowances to 26 TLRs. Head of year posts are to be abolished.
Paul Davis, the head, said he had followed national guidance supported by the union.
Chris Keates, the NASUWT general secretary, said: "We will take action where heads or governors seek to save money or disadvantage individual members of staff because their face doesn't fit."
Its members have held four one-day strikes and are now threatening a work-to-rule in three Stoke secondaries over claims that about 10 staff were wrongly denied progression to the UPS3 pay grade and a pound;1,100 pay rise.
Mick Brookes, general secretary of the National Association of Head Teachers, said: "There are those who see TLRs as an extremely useful tool for restructuring the management of their schools. But others believe it will depress and demoralise their staff. We have serious concerns about the levels of stress this is causing."