Just over a million employees earning up to 34,189 are being asked to give up annual increments – on top of an existing two-year pay freeze – in return for a guarantee of no compulsory redundancies.
The number facing the axe if the deal was rejected has been set by NHS Employers – which represents primary care trusts and other providers – at 35,000.
Increments were previously excluded from the original public sector pay freeze, which affects all but those earning less than 21,000, and are worth up to a few thousand pounds a year.
Ending them for two years would, NHS Employers calculates, save 3.8bn as part of the effort to secure 20bn of efficiency savings in the health service by 2014/15.
Karen Reay, national officer for health at the Unite trade union, said: "If you don't accept these swingeing proposals, other people may lose their jobs. This is a blunt threat by employers and a negatively emotive way of trying to do business.
"Staff who are loyal to the NHS and aren't paid too much to start with are now being asked to take another hit. It's unfair. Many are angry that, after the two-year pay freeze, they are expected to lose their pay increments for two years as well."
The deal was first proposed earlier this week, with doctors' leaders saying it exposed Government claims the NHS budget was being protected as false and expressing doubts about the offered job loss guarantee.
"This proposal makes clear that the NHS is in fact facing a real-terms cut in funding over the next two years and it appears NHS staff are expected personally to bridge the funding gap in some way," Hamish Meldrum, chairman of the British Medical Association Council said in a letter to members.
The guarantees "appear to be very limited and will be left to local agreement", he noted.
A Department of Health spokesman was not immediately able to confirm the 35,000 figure.
He added: "We welcome discussions between NHS Employers and staff on issues concerning pay progression and jobs during the spending review period.
"The discussions are being properly considered by NHS Employers in partnership with the NHS trade unions through the national NHS staff council. We will consider very carefully any formal proposals when they are made."