NSW Prisons will introduce a new, super-security prisoner rating to stop subversion and illegal activity by the state's most dangerous inmates.

The announcement by the Attorney-General, John Hatzistergos, came as two convicted murderers allegedly involved in a plot to lead a mass breakout from Goulburn's Supermax prison began legal action against their imprisonment.

Mr Hatzistergos said the new prisoner designation of "extreme high risk restricted" would be "over and above" the existing high security and extreme high security classifications of 101 prisoners in maximum security jails, including those at Goulburn, Long Bay, Parklea and Lithgow.

It would also be separate to the AAA anti-terrorist category created for those who pose threats to national security.

Those identified from prison intelligence as a subversive threat would face extra security measures including no contact visits and all visitor conversations and one phone call a week to be conducted in English or another approved language. Their visitors must have approval and undergo criminal record checks, and any money sent to an inmate's prison account would be returned.

Yesterday Bassam Hamzy, the alleged ringleader of the so-called "Super Max jihadists", and Emad Sleiman obtained leave to file a claim for wrongful imprisonment in Supermax in the NSW Supreme Court.

Hamzy, now in Lithgow jail, and Sleiman argued their segregation represented unlawful imprisonment.

If successful, the motion could force the closure of Goulburn's high-risk-management unit known as Supermax, regarded as Australia's highest security complex, because it would be deemed to be a prison within a prison.

The prisoners might also be able to sue the Corrective Services Commissioner, Ron Woodham, for damages if they were wrongfully imprisoned.

Hamzy, a devotee of Osama bin Laden, is serving a 21-year sentence for a 1998 shooting murder outside a nightclub.

The new designation was branded as "appalling" by the NSW Greens MP, Sylvia Hale.