Leading Real IRA figures are among up to 800 prisoners suing the Irish Government because they do not have flushable toilets in their cells.
The prisoners claim slopping out breaches their human rights
The Irish Department of Justice has said it will vigorously contest the claims, which could cost millions of euros.
The prisoners and 35 prison officers are claiming they suffered trauma because of slopping out - a system where inmates are given chamber pots and plastic containers for toilet use which they have to empty in the morning.
Prisoners involved in the action include former Real IRA Director of Operations Liam Campbell, its Munster Chief of Staff James Bowman, Republican Sinn Fein Vice President Des Long and convicted drug dealer Patrick Holland.
The Limerick-based solicitor representing the group, John Devane, said prisoners were entitled to dignity, and should not have to slop-out.
'Human rights breach'
The claims follow a Scottish legal ruling in April where a prisoner was awarded £2,400.
Robert Napier, a remand prisoner at Barlinnie Jail in Glasgow, had claimed that the practice breached his human rights.
He raised a legal challenge in 2001 under the European Convention on Human Rights, in which he sought £5,000.
Napier said the conditions had aggravated his eczema and resulted in a "diminishment of his human dignity".
In his judgement, Lord Bonomy found that slopping out violated articles three and eight of the convention and the common law "duty of care".
On the violation of article three, the judge said: "I am entirely satisfied that the petitioner was exposed to conditions of detention which taken together, were such as to damage his human rights, his human dignity and to arise in him feelings of anxiety, anguish, inferiority and humiliation."