Families of dozens of teenage prisoners being held at Western Australia's high-security adult prison at Hakea are taking legal action to have them moved.
Some 140 juvenile offenders are still being housed in the high-security jail after nearly 100 cells were destroyed in a riot at the Banksia Hill juvenile detention centre in January.
Three inquiries are looking at how and why the prison was trashed.
But after submissions by WA prison inspector Neil Morgan expressed grave concerns about how young prisoners were being treated, human rights lawyer George Newhouse will launch a landmark legal action on Wednesday.
Mr Newhouse, acting on behalf of the family of one young offender, will allege the housing of young offenders in segregated units at Hakea Prison breaches the state's Young Offenders Act.
"There are major issues there, and given the conditions we will be asking the court to deal with the matter as quickly as possible, but that is a matter for them," Mr Newhouse told AAP.
"You don't have to take my word on it, given WA's Commissioner for Children and Young People and the Chief Justice of the Children's Court have both slammed the decision to move the children there."
The legal action will be made against the state's Corrective Services Minister and the Corrective Services Commissioner, and is set to be lodged at the WA Supreme Court today.
After being sworn in last week, WA Prisons Minister Joe Francis promised to deal with the issue as a matter of urgency, but he has so far declined to comment.
Concerns were raised by Amnesty International, lawyers from WA's Legal Aid and prison officers said teenage prisoners were being abused by officers, seeing family and lawyers less, and losing weight because of a lack of food.
It was alleged one young prisoner had his head shoved down a toilet by an adult prison officer while being restrained and another attended had court with cuts and bruises after being thrown from a prison van onto the ground.