Advocates said inmates were protesting against unhygienic and dehumanising conditions - claims denied by Corrections.
On Wednesday Te Paati Māori co-leader Rawiri Waititi said each of the 16 prisoners involved had filed a claim in the High Court at Wellington against the Attorney-General and the chief executive of Corrections for breaches of their civil rights, the Treaty of Waitangi, the Corrections Act 2004, and the United Nations Standard Minimum Rules for the Treatment of Prisoners (the Nelson Mandela Rules) 2015.
Fourteen of the prisoners who were Māori had also filed claims against the Crown in the Waitangi Tribunal.
"The facts will show that the prisoners have been treated inhumanely and with extreme cruelty by Corrections' staff," Waititi said.
"For months, the men had been denied the right to complain about their conditions because staff would not give them the standard PCO1 complaint forms."
Waititi said this included poor water quality, unsanitary bedding and extended use of 23-hour solitary confinement that breached UN conventions.
There had been numerous reports into the poor state of the prison - and others - which Waititi said showed a "trend".
"We will not allow them to hide behind this very racist system that continues to keep Māori at the bottom.
"We are ensuring [the prisoners] get legal support they need, to ensure their voices are heard."
Last August, the Ombudsman published a report following an unannounced inspection of Waikeria which found the high-security areas were old, not fit for purpose, and in some cases failed to meet minimum UN standards.
The Ombudsman found meal times across the prison did not reflect usual meal times, and many inmates voiced concern about water quality.
Some cells were run down, with chunks of vinyl missing from floors, some windows did not have curtains and toilets did not have lids.
Peter Boshier later described the conditions in the "top jail" - which was destroyed by the riot - as "decrepit" and "bordering on inhumane".
The Human Rights Commission also called for an inquiry to be launched into the incident.
Chief Commissioner Paul Hunt said it was a mistake to see it as an isolated one-off.
"Whatever triggered this protest, poor prison conditions are a vital part of the context.
"Last August, the Ombudsman published a report on Waikeria and concluded that the high-security complex is no longer fit for purpose.'
