The High Court has ruled that a smoking ban in Auckland Prison is unlawful, invalid and of no effect.
A career criminal brought the civil case against the prison's manager after cigarettes, lighters, matches and tobacco were banned in all prisons in July last year.
The High Court says the prison managers had no authority to introduce that rule.
The Corrections Department says the ruling does not change the status quo and new regulations came into force last month, making tobacco in prisons contraband.
Corrections Minister Anne Tolley said the ruling is being considered and if the Government needs to change the law to maintain a smokefree environment in prisons, it will do so.
The Corrections Association said the ruling will confuse the prisoners.
Prison Service general manager Brendan Anstiss said about 6000 prisoners are no longer spending their money on an unhealthy habit - so the smoking ban is still the right thing to have.
The department says it will fight any further legal challenges to the ban.