Health workers are threatening to revolt over a government plan to shake up the NHS in return for a phased pay increase of almost 16%.
Rejection would be a bitter blow to Alan Milburn, the health secretary, who sees the deal, known as Agenda for Change, as vital to improve the way 1.2m staff do their jobs.
Opposition will erupt in public next week in Harrogate at a conference of NHS employees in Unison, the biggest NHS union.
Unison's leadership is proposing acceptance of the deal, which would see a 10% rise over three years plus an extra sum of up to 5.9% for many workers. It is also supporting trials on new ways of working in a dozen health trusts.
Two ballots of members in the health service are proposed, but opponents of reform are calling for rejection of the 10% and withdrawal of co-operation with the trials, due to start in the next few weeks.
Such a rebellion - on the eve of a one per cent rise in national insurance contributions to fund a record jump in health spending - could plunge the NHS into a new round of disputes, just when Mr Milburn had hoped a breakthrough had been achieved.
Reforming how staff work is considered essential to most of the government's plans for the NHS, and the Agenda for Change package was discussed over four years with 17 unions and professional associations.
The deal would see 650 grades whittled down to eight pay bands, with 5.9% over five years added to wages for those judged winners in a major job-evaluation exercise.
However, a growing number of employees fear they would lose out and be forced to do more work for little or no extra money. A three-year 10% pay offer, with 3.225% from April as a first instalment, now also looks less attractive following recent inflation figures showing a rate of 3.2%.
Unison's health group executive has voted by a two-to-one margin to back acceptance of the 10% and cooperate with the Agenda for Change trials.
Dave Prentis, Unison's general secretary, admitted that some members were unhappy.
"As with any job evaluation scheme there will be groups that gain and some that won't do as well," he said. "We want to make sure that all NHS workers are treated fairly in this exercise so that morale is restored and we can then get on with delivering the best health service."
But Geoff Martin, convenor of Unison in London, said: "We have to ask what national negotiators have been up to. No one should underestimate the level of anger at the sharp end of the health service."
Mr Milburn has described Agenda for Change as the "most radical modernisation of the NHS pay system since its foundation in 1948" when details were published in November. Prominent union negotiators were angry, saying the government had "jumped the gun" by releasing the figures before the details had been finalised, in an attempt to put pressure on the firefighters during their industrial action.
A report today by the research group Income Data Services will fuel opposition to the pay offer - showing how little it was worth in real terms.
"The higher rate of inflation is starting to push up private sector pay settlements just as government pressure has lowered public sector pay increases awarded so far this year," says the report. "The increase of 2.9 % for teachers, 2.8% for prison officers and the offer of 3.225% for one million NHS employees, all to take effect from April, now look decidedly modest against the backdrop of annual inflation at 3.2%."
