There have been over 800 prisoner-on-prisoner assaults in Northern Ireland in three years.
Half happened in HMP Maghaberry alone, the BBC Nolan Show revealed today.
Paul Frew, a member of the Justice Committee, said: "It's very, very worrying that we have levels of staff that can't control prisoners."
"Usually in a well-run prison there would be about four staff for 50-60 prisoners. But on one occasion in 2015 there was one staff member on landing with 80 prisoners.
"Staff are leaving, on long-term sick because of the stress, the extra load and pressure being brought to bear on them. We have now got voluntary exit scheme coming up where there would be as many as 360 staff wanting to leave."
In November an inspection report described Maghaberry Prison as the most dangerous ever inspected by Her Majesty's Chief Inspector of Prisons.