Two wards may be closed in a shake-up at a Cambridgeshire hospital.
Managers at Hinchingbrooke plan to close gynaecological and medical wards to finance a £30m treatment centre.
Chief executive Douglas Pattisson said there would be no net loss of beds but staff say the unsettling move has come out of the blue.
The unions say they will work with the hospital to see whether the wards can be kept open and if savings could be made elsewhere.
Patients using the new diagnostic unit will have routine surgery there and go home within 24 hours. It means redeploying dozens of staff .
Chief executive Douglas Pattisson said: "We're opening 46 new beds in the new treatment centre and we're taking 46 beds out of the main body of the hospital.
"At the moment there's no net loss at all - the important thing is we're treating more patients than ever before."
Chris Marshal, of the Unison union, said: "The new unit won't open until October so there's a little bit of re-arrangement within the hospital, and that's where the uncertainty lies -the fact that it's come out of the blue to members of staff."
Ward sister Ann Seeds, of the Royal College of Nursing, said staff and the hospital trust was meeting early next week.
"I think that's going to be very important to safeguard patient care and our members who are working here," she said.