Relatives of high-risk terrorism inmates being held in the state's most notorious prison claim the prisoners are on a hunger strike in protest at a new rule preventing them from speaking Arabic.

Prison officials have strongly denied any strike is taking place and have refuted other claims that Korans and prayer time have been taken away.

On Sunday, NSW Attorney-General Brad Hazzard announced the policy banning 13 "extreme high-risk" terrorism inmates from speaking any language other than English during family visits, phone calls and in letters.

All visits have also been restricted to non-contact, and previously approved visitors are being vetted again.

Family members claim the ban is discriminatory, inhumane and clearly applies only to Arabic because the 13 terrorism inmates are all Arabic speakers.

"This is a concern for some inmates who don't speak much English but a greater concern as this means recitation of Quran and Hadith [prophetic traditions], and duaa [prayers] in Arabic could be stopped and made punishable by prison guards," said a Facebook page, Oz_cage Muslim Prisoners, set up by family members of the inmates.

Among the 13 extreme high-risk inmates are members of the foiled Pendennis terror cell Khaled Cheikho, Moustafa Cheikho, Mohammed Omar Jamal, Mazen Touma and Omar Baladjam.

The operator of the Facebook page, believed to be a relative of the Cheikhos, said 11 Muslim inmates were refusing to eat, take visitors or leave their cells for outdoor time.

"It's not just about the Arabic, it's more than that," he told Fairfax Media.

He said a relative of one inmate contacted him to say that prison guards had confiscated Korans and would not allow inmates to pray.

A spokesman for Corrective Services NSW strongly denied there was a hunger strike or that guards had taken Korans and banned prayer time.

He said the new policy was not discriminatory and the ban on foreign languages applied only to visits, phone calls and letters, not prayer or religious practice.

"The restriction on language is necessary for security reasons, and is not discriminatory as it applies to all languages other than English," he said.

Commissioner for Corrective Services NSW Peter Severin reiterated on Wednesday that the rules don't apply to the wider prison population or to prayers.

"These changes have been implemented to ensure as far as is possible the community is safeguarded," he said.

Terrorism inmates are given their own classification, AA, and kept in the Goulburn Supermax, the most secure facility in the state.

Mr Hazzard said that, after individual cases has been reviewed, 13 AA inmates had been classified as Extreme High Risk Restricted to be subjected to the new restrictions.

It is believed this includes men on remand who have not been convicted.

Two siblings of Sulayman Khalid, who was arrested in December for allegedly planning a terrorist attack, posted on Facebook that their brother told them via phone that he was striking because of the restrictions.

The 19-year-old's family have previously told Fairfax that he had been denied any contact with the outside world, despite not having been convicted.

In Goulburn's High Risk Management Unit, inmates are under constant supervision, take and make phone calls in a wire cage and, when moved about, are shackled and escorted by up to four prison officers at a time.

Mr Hazzard said the number of terrorism inmates was increasing and the new restrictions were needed to "prevent inmates ... from co-ordinating terrorism activities or inciting extremism from inside prison".

"While there is no known specific terrorist threat from inside our prisons, these inmates' communications from prison have the potential to have a direct impact on national security and community safety.

"That's why I want to make sure we know at all times who they are talking to and what they are saying," he said.

The Corrective Services NSW spokesman stressed that the restrictions banned all languages other than English, not just Arabic, and the commissioner can give permission for another language to be spoken in special circumstances.

For example, if a prisoner's elderly parents didn't speak English, Arabic may be spoken with an interpreter present.

Lawyer Adam Houda tweeted that the ban on Arabic was "barbaric, cruel & discriminatory" and cut many prisoners off from their families.

He said he would be challenging the rule.

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CORRECTION: An earlier version of this story has been amended to state the 13 AA inmates were classified Extreme High Risk Restricted by the Commissioner for Corrective Services, not by the Attorney General and Minister for Justice, Brad Hazzard.