The Corrections Association, which represents most prison officers, has alerted emergency services to the risk of riots, once inmates lose the right to smoke from July.
There was unrest in Australian prisons when a similar ban was tried.
Roughly 8700 people are currently being held in prisons and it is thought about two-thirds of them are smokers.
The union has contacted the police, ambulance and fire service to warn they may be called upon if the prisoners riot.
The Corrections Department is downplaying the likelihood of trouble, saying about 2000 inmates are now on nicotine replacement therapy.
The Quit Line phone service had only 86 calls from prisons in January, 61 in February and 87 in March.