New figures on the religious breakdown of Northern Ireland's prison population have shown that a disproportionate number of Catholics are behind bars.
A major review that recommended overhauling the prison system, also raised concerns over the monitoring of inmates' religion, race and disability.
Figures compiled for the report showed that while Catholics make up 44% of the general population, around 55% of inmates are drawn from the Catholic community. The report said it could find no clear explanation for the disparity, but said it may be the case that there are higher numbers of Catholics among younger age brackets in Northern Ireland.
The figures showed that 56% of prisoners in Hydebank Wood Young Offender Centre were Catholic, while 54% of prisoners at Maghaberry prison were Catholic, with 56% of inmates in Magilligan being Catholic.
Prisoners held on basic privileges, as opposed to enhanced status, were also more likely to be Catholic with a 74% figure for Hydebank, 66% in Maghaberry and 82% in Magilligan.
The report found: "Overall, Catholics were also disproportionately represented in matters relating to prison discipline - adjudication, use of force and segregation.
"In Hydebank Wood and Maghaberry, Catholics were disproportionately unlikely, and Protestants disproportionately likely, to be granted temporary release, for healthcare, emergencies or resettlement reasons.
"It also appears to be the case at Maghaberry that Catholic prisoners are over-represented in the poorer accommodation on the 'square houses' and Protestants over-represented in the newer and better units."
The review team said it was "very disappointing" that some of the discrepancies identified were also picked up in a report in 2008.
It added: "But monitoring is pointless if it does not highlight problems and lead to action to investigate and if necessary rectify them. Given the importance of being able to demonstrate equal treatment in Northern Ireland, this is a significant gap."