A fresh counter-terrorism crackdown has been launched across NSW prisons which could force lower-security inmates to use English when writing letters, speaking on the phone or talking with visitors.

The state government on Friday created a new prisoner designation – a "national security interest inmate" (NSI) – to crack down on prisoners deemed at risk of inciting or organising terrorism via their contact with the outside world.

Federal Attorney-General George Brandis has said the Commonwealth will introduce legislation to lower the control order age threshold. Credit:Alex Ellinghausen

The new powers allow NSW Corrective Services Commissioner Peter Severin to impose severe restrictions on the ability of prisoners who have not been convicted of terrorism offences to communicate with visitors, friends and family.

The powers could see minimum security inmates hit with some of the same restrictions as high-risk inmates already convicted of a terrorism offence.