New figures reveal serious assaults on prison guards have tripled in the past five years.
During the year to the end of June, 18 staff were seriously assaulted - up from just six in 2007.
And 235 cases of physical violence - which includes prisoners spitting or throwing water - were recorded in the past year, a rise of 190%on two years ago.
The Government has disclosed the statistics in a response to a written parliamentary question from the Labour Party.
Labour's justice spokesperson Charles Chauvel says the figures are a considerable worry, particularly given that the overall prison muster has dropped significantly.
Mr Chauvel says Corrections must outline what it's doing to reverse the trend, for the safety of prison officers.