Loyalists have threatened to take the British government to court over conditions for paramilitary prisoners at Maghaberry Prison.
Representatives of Ulster Volunteer Force and Red Hand Commando inmates held under new £7 million arrangements at the Co Antrim prison claimed they were being discriminated against.
Loyalists and republicans at the bitterly divided complex near Lisburn have been separated amid major security fears.
Prisoners who demanded segregation were allowed to be kept apart once they signed up to the terms laid out by the authorities.
But the Post Conflict Prisoners Support Group claimed exercise and health facilities in the specially equipped cell blocks were not up to standard.
Spokesman Mr Ken Wilkinson said: "We're not asking for the moon and the stars, all we want is to be treated equally.
"One of our prisoners will be taking a judicial review on the basis of the discrimination in separated wings compared to the rest of the jail."
Mr Wilkinson revealed plans to contest the scheme as he prepared his group's response to plans to bring in new prisoner complaints procedures and an ombudsman.
Although he praised the proposals, the loyalist spokesman insisted the separated prisoners issue was now critical.
The British government agreed to bring in extra guards and install extra security at Maghaberry, which holds Northern Ireland's most notorious terrorists and criminals, after an intensive and violent campaign by both sides.
