The Corrections Department has been ordered to further consult a prison officers' union about an 8am - 5pm shift on staff rosters.
The Department introduced the new shift to the roster last year, so that prison guards hours' align with the hours during which inmates are unlocked.
The Corrections Association complained the roster change breached its collective agreement on health and safety grounds.
But the Department argued the matter was a policy which it was entitled to create after local discussions at individual prisons.
The Employment Relations Authority has now ruled the consultation should have been conducted at a national level.
The Authority says the Corrections Department must now ask the union about the nationwide roll out of the roster change.
A Corrections Department spokesperson says the 8am - 5pm unlock regime will continue for now and a meeting with the union will be sought.
