Staff at two hospitals have been invited to resign as part of a drive to reduce the workforce.
A Mutually-Agreed Resignation Scheme (MARS) began on Thursday at Northampton and Kettering General hospitals.
The University Hospitals of Northamptonshire (UHN), which run both sites, said the scheme was designed to avoid compulsory redundancies.
A union has said it had "real concerns" about the move.
A MARS arrangement enables employees to agree with their employer to leave the organisation in return for a severance payment.
Unlike voluntary redundancy, MARS does involve a formal consultation process.
Workers at both hospitals have been told about the scheme this week.
UHN's chief executive Laura Churchward said: "This voluntary scheme is designed to help reduce our workforce size in a controlled and compassionate way, avoiding compulsory redundancies.
"Colleagues who are caring directly for patients are not in scope of the scheme, and each application will be carefully considered to enable us to deliver more efficient services that continue to meet the needs of our patients."
The scheme will only be open to those in corporate, administrative and support roles.
A spokesperson for the union, Unison, which represents some workers at the hospitals, said: "NHS staff in Northamptonshire are already overworked. Paying off hundreds of staff will only make this situation worse.
"We have real concerns about what this will mean for the staff who resign under this scheme, for their colleagues who are left to pick up the pieces, and the patients who rely on vital services."
As first reported in the Northamptonshire Evening Telegraph, a Kettering nurse said compulsory redundancies could not be ruled out if not enough people applied for MARS.
The nurse added that the workload in department where staff agreed to leave would be shared among the remaining team.
NHS rules require MARS schemes to be open for no longer than three months.
