According to 2002 figures, around 3,450 teachers who moved jobs after school closures or local authority reorganisations benefit from locally-agreed salary "safe-guarding" arrangements, which are not time-limited.
In September, teaching unions - but not the National Union of Teachers and Welsh union UCAC - signed a deal with the Government and employers agreeing that all such arrangements should end in three years.
But, as TES Cymru revealed in May, the NASUWT and Association of Teachers and Lecturers have been negotiating an eleventh-hour reversal.
Now all future safeguarding deals will be limited to three years by the schoolteachers' pay and conditions document. But, subject to a consultation which closed last month, existing arrangements are to be protected.
Classroom unions welcomed the change.
But one heads' leader has written to Ruth Kelly, Education Secretary, saying that the U-turn will make it more difficult for heads to manage their budgets. Pay and conditions are not devolved to the National Assembly.
Peter Hudman is one of those likely to benefit. He has had two management allowance points, worth pound;3,312, protected since 1993 when his job as a secondary science specialist on Bradford council's supply teaching team was cut. Now on secondment as an NASUWT health and safety officer, he said:
"If the details are confirmed, I will have a great sense of relief. Recent teacher pay rises have not been keeping pace with the cost of living and I couldn't cope with a further cut."
But David Hart, the National Association of Head Teachers' general secretary, said: "The idea of still receiving a safeguarded salary as a result of a reorganisation that took place in 1985, for example, would be seen as absolutely amazing by any other employer."
His letter to Ms Kelly warns that the new statutory duty on schools to find extra duties for teachers on safeguarded salaries would inhibit heads from allocating responsibilities to those best equipped for them.
Mary Bousted, ATL general secretary, said: "Members entered into permanent safeguarding arrangements in good faith and we argued that those agreements should be honoured. We are delighted that the Secretary of State has seen the strength of our argument."
Chris Keates, the NASUWT's general secretary, who has said it had always been agreed the safeguarding issue would be looked at again, said that she thought about 3,000 teachers would benefit from the change.
* This week, official figures revealed that the NASUWT and the ATL closed the membership gap with the largest teaching union, the National Union of Teachers, in 1994, Union figures 6