The government is planning to cap headteachers' pay to the pound;142,500 salary of the Prime Minister, The TES can reveal.
Education Secretary Michael Gove's clampdown on senior wages comes only weeks after the announcement of a two-year public sector pay freeze brought the spectre of teachers' strikes onto the horizon.
The cap would end a period of rapid growth in headteacher pay, prompted by the expansion of the academies programme and the numbers of executive heads running more than one school.
Around 100 heads are thought to be earning in excess of pound;150,000, with a handful believed to be receiving as much as pound;180,000. In academies, headteacher jobs paying six-figure salaries and performance bonuses have become the norm, even outside London.
But Mr Gove wants to bring heads' pay into a wider drive to push down large public sector pay packets.
In a letter to Anne Wright, chair of the School Teachers' Review Body (STRB), which advises the Government on pay, Mr Gove said he wanted to consult on his view that "salary should not exceed that of the Prime Minister". The plan is for the cap to be imposed on new pay deals as early as this September.
The STRB does not cover academies, but the Government is investigating ways to impose the cap on academies as well to prevent a two-tier system. Unions say it is "at odds" with Mr Gove's desire to give schools greater flexibility over teachers' pay.
Currently, the top of the pay scale in the largest London state schools is supposed to be set at pound;109,658. But the law effectively allows governors in the largest schools to offer whatever pay they need to in order to attract the right candidates.
Jacqueline Valin, executive head teacher of Southfields Community College, an "outstanding" comprehensive in south London bidding for academy status, said recruitment would be badly affected if pay was limited to pound;142,500.
"Governors need the freedom to go into the marketplace and attract the best person," she said. "Recruiting is extremely difficult, as has been proven time and again."
One highly paid head of an east London comprehensive of 1,700 pupils, who asked not to be named, said: "Headteachers who are earning that much or more have a lot of experience, have system-wide responsibilities across groups of schools and a track record of achievement, so to put any official limit on their salaries is counterproductive."
Malcolm Trobe, policy director at the Association of School and College Leaders, said: "No one disputes the fact there's a level above which the responsibility of a headteacher won't merit a salary above a certain level, but it should be decided by a pay review body, not an arbitrary figure such as the PM's salary."
Despite pressure from unions, no figures are currently published on how many heads earn more than the top of the pay scale.
As reported in The TES last week, heads are also being excluded from the fair pay review, commissioned by the Government, which will investigate pay scales across the public sector.
A spokesman for the Department for Education said: "The Chancellor is clear that the country is living beyond its means; that the entire public sector must share the burden of dealing with the growing national debt; and that if we don't tackle pay and pensions, more jobs will be lost."
He said that while academies are in general free to set their own staff pay, "we feel there is a strong case for ensuring no principal of an individual academy earns more than the Prime Minister and are speaking to academy representatives to agree how best to give this effect".