Headteachers are threatening industrial action for the first time in the history of state education because of a lack of funding for the Government's performance-related pay scheme for teachers.
The executives of two headteachers' unions, the National Association of Head Teachers and the Secondary Heads Association, will vote on a boycott of the scheme this weekend.
Heads are angry that the Government has provided enough funding to give only half the 200,000 senior teachers eligible for a further £1,000 rise this September their increase.
John Dunford, the general secretary of the Secondary Heads Association, said: "The decision to restrict the funding will only demoralise teachers further. If you've got a school where 40 teachers are eligible for the rise and you can only pay 20, how can you distinguish between them?"
The move comes as ministers are trying to win support from headteachers for a shake-up of the school curriculum to be announced next week.
David Hart, the general secretary of the National Association of Head Teachers, said: "There is a depth of feeling on this issue. If they were to fund all the rises, they would have to take the money from elsewhere in their budgets, which could mean cutting jobs."
Under the scheme, teachers at the top of the pay scale are eligible for a £2,000 rise and thereafter £1,000 rises. The Government has earmarked £250m for the next few years, but headteachers say it will cost £450m to meet the payments.
They say it would be impossible to deny £1,000 rises to teachers who have qualified for £2,000 rises. If there is a boycott, heads will refuse to assess if the staff get £1,000 rises.
A spokeswoman for the Department for Education said: "It is quite wrong for headteachers' unions to threaten a boycott ... Teachers have a right to expect their performance to be regularly assessed."
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