A prison warden was sacked for interfering with an inmate's letter.
The culprit was among 30 cases of suspension or dismissal for gross misconduct in three years, the Prisons' Minister confirmed.
Harassment, expenses fraud and even an inappropriate relationship with a prisoner were also among the offences, Paul Goggins added.
He has called for change after a report criticised officers over the death of Colin Bell, 34, who hanged himself while on suicide watch at Maghaberry prison, Co Antrim, in August last year.
SDLP Assembly member Dolores Kelly said: "Very few people are concerned about prisoners' welfare and society ought to be judged on the treatment of their prisoners.
"The failings that have been found... led to the conclusion that the best way forward is for a full review and reform of the whole prison system."
The number involved in disciplinary proceedings was a minority of the overall staff. Some of the 30 cases may have been counted twice, involving a suspension and a dismissal of one person for one offence, while many related to the death of Bell.
Ms Kelly has appealed for a Patten-style commission on prisons.
Tony Pearson headed a panel considering the future of the prison service which published 38 recommendations yesterday.
He acknowledged the dangerous work which prison officers had carried out during the years of the conflict but said it was time to shift from the heavy emphasis on security.
Bell, serving life for murder, was able to kill himself despite a history of disturbed behaviour.
He was on suicide watch and was to be monitored every 15 minutes yet his body was only discovered 40 minutes after his death.
Video camera footage showed some staff lying in bed watching television while they were supposed to be on duty.
Ms Kelly added: "People need to have confidence in all of the partners in the criminal justice system and I don't think that there's that level of confidence or support."
She criticised the treatment of Catholic prisoners, which was recently highlighted in a separate report.
Figures revealed by Mr Goggins following a written parliamentary question from Lady Sylvia Hermon disclosed the details for 2006-08. They included seven dismissals and 23 suspensions, some for police investigations, others for fraud.
In 2008 there were 17 suspensions, many for neglect of duty following Bell's death and one for an inappropriate relationship with a prisoner.
An officer responsible for interfering with a letter was dismissed as was one who entered an inappropriate relationship with a prisoner.
A spokesman for the Prison Service said all employees of the Northern Ireland Prison Service are expected to meet high standards of personal conduct.
"The adherence to these conduct standards is fundamental to the integrity and proper workings of the service. Any failure to meet them undermines the work of the service.
"The commitment to upholding standards of conduct in the service is underpinned by disciplinary procedures which provide a fair method of dealing with alleged misconduct."
The code of conduct and discipline sets out the standards required of staff and how any allegations or suspicions of misconduct are dealt with.
The spokesman added: "The service has a workforce of over 2,300 and the vast majority of staff have exemplary records.
"However, where it is found that a member of staff has breached the code of conduct and discipline appropriate action will be taken. It is a matter of deep regret that the service has found it necessary to dismiss seven members of staff in the last three years."