Up to 4,000 managers and administrative staff will be culled from the Health Service Executive (HSE) under a new proposal.
The Government revealed the 400 million euro voluntary redundancy and early retirement schemes will be offered to more than 28,000 staff members.
Some support personnel, such as chefs and porters, will also be included in the schemes - which must be applied for by November 19.
The Siptu trade union described the move as another black day for the health service.
Paul Bell, acting head of its health division, claimed the HSE appeared to have no idea how the health service would function with 4,000 fewer staff.
"It is another black day for the health service," said Mr Bell.
"The plan prepared after consultation with the departments of health and finance envisages that 4,000 clerical, administrative and support staff would leave the service by the end of November.
"There is no provision for the hole that will be left in the service when these people have departed."
The union stressed it will not accept the backfilling of the service by contract or agency staff.
Health Minister Mary Harney maintained the schemes will secure permanent staff reduction and facilitate health service reform. They will be open to management and administrative grades and support staff who must retire or resign by December 30.