HASLAR detention centre is set to become a prison, The News can reveal.
Immigrants being held at the Gosport facility awaiting deportation will be moved to other centres by May.
Staff face being sent to prisons out of the area after negotiations over jobs are held with unions.
Bob Coleman, chair of Haslar’s independent monitoring board, said staff were offered positions elsewhere.
Mr Coleman: ‘It’s a huge blow for them.
‘The vacancies being thrust at the staff were not in the locality, they were up in the north of England.’
Many staff moved to Haslar from Kingston Prison when it closed in 2013, he added.
Haslar is run by the Prison Service for the Home Office but will be handed back to the National Offender Management Service.
The Ministry of Justice said staff who are redeployed can join a detached duty bonus scheme and will be eligible for another bonus scheme, if it is run in the prison.
The Prisoner Officers Association has criticised the scheme saying it forces workers away from their families.
No spokesman was available yesterday.
A Home Office spokesman said: ‘Detaining and removing people with no right to be in the UK, with dignity and respect, is an essential part of maintaining effective immigration controls.
‘That work requires an estate of modern, secure centres located with easy access to the airports.’
Centres in the south east will take detainees from Haslar and the change will save cash, he added.
Security and immigration minister James Brokenshire wrote to Gosport MP Caroline Dinenage yesterday.
Ms Dinenage said: ‘My priority is to find out what will happen to the people employed at that site.
‘I’m making an urgent appointment to discuss this in more detail with the minister.’
Staff were told it could open as a prison by 2016 but the MoJ said it will ‘when required’.
Figures last month showed there were 173 men in the centre.
No new detainees will be moved to Haslar ahead of the closure.
Capacity was increased from 160 to 197 last summer at the Dolphin Way facility.
Friends Without Borders – formerly Haslar Visitors Group – has worked with detainees for 20 years.
Co-ordinator Anne Dickinson said there was a trend toward housing detainees in larger centres but they were difficult to manage and could lead to problems.
‘I’m not surprised a smaller centre has been closed,’ she said.
Haslar was first an army facility then a young offender detention centre.
It has held immigration detainees since 1989 and was designated a removal centre in 2002.