More than 350 prison officers in Northern Ireland have taken sick leave in the past three years because of depression and stress, it has been revealed.
A warders' representative warned that more are at risk due to a continuing dissident threat.
Finlay Spratt, chairman of the Prison Officers' Association (POA), said the murder of David Black, ambushed by gunmen as he drove to work on the M1 last month, added to mounting pressure within the Prison Service.
Staff from governor rank down to the lowest levels were affected by the increasing stress burden, said justice minister David Ford.
Mr Spratt said: "There's no doubt about it that David Black's murder had a major impact on staff in the Prison Service, and that really brought to light the reality. If you are a prison officer, it does not matter where you are serving, you are open to these attacks."
Mr Ford told the Assembly that the 356 affected ranged from governors, principal and senior officers, to those in operational support grades like drivers. His answer was in response to a written question from Alex Easton, DUP MLA for North Down.
Between November 2011 and last month, 125 officers took leave, an increase of nine workers on the previous year, Mr Ford said.
In September 2009, then governor at Maghaberry Steve Rodford resigned amid threats to his safety after his personal details were found in a cell belonging to the man convicted of murdering Constable Stephen Carroll.
With a continued dissident threat against prison officers, Mr Spratt said he does not believe there will be a decline in the numbers affected by stress and depression.
He added: "I predict to see the stress levels rising among prison officers and I believe this will continue to rise, as it did throughout the Troubles when there was a lot of stress. Prison officers are being treated the same as civil servants who work Monday to Friday."