Trusts have been urged not to settle back pay claims from women who claim they were unfairly treated before the introduction of Agenda for Change.
The Department of Health has told trusts not to settle any of the 13,000 claims making their way through employment tribunals until the legal position has been clarified.
They are mostly being brought by women who argue they were paid less than men for doing equivalent jobs before the introduction of Agenda for Change, which brought in new pay arrangements for most NHS staff.
In a bulletin to managers, NHS Employers said it was a 'common misconception' that women and men who are now on equal pay under Agenda for Change could argue for up to six years' back pay for past unequal treatment.
An NHS Employers spokesman said the warning arose following a case in November 2006, known as the Bainbridge ruling, where staff from Cleveland County Council lost the right to back pay.
The staff won a discrimination case at the Employment Tribunal but lost their back pay claim at the Employment Appeals Tribunal.
Other legal issues also need to be tested, NHS Employers said, such as whether applicants in one trust can compare themselves to an employee in another trust. Trusts should not 'settle any claims until the legal issues are resolved'.
Solicitor Stefan Cross, who represented staff in the Cleveland case, said he would resist the move on behalf of more than 10,000 NHS claimants.
'Trusts really want to have their cake and eat it. On one hand, they want to say that jobs are not of equal value based on the banding prior to 2004. On the other hand, they are saying that there is no entitlement even if they have been banded the same post 2004,' he said.