The protesters were arrested last week during demonstrations at industrial parks in the capital, the Phnom Penh Post reported Thursday.
Family members, lawyers and a doctor were not allowed to see them until Wednesday. Relatives said authorities had refused to confirm the identities of those being detained or say where they were being held.
The actions by the government, including holding the protesters in a remote prison far from their homes, broke Cambodian law, said Naly Pilorge, director of rights group Licadho.
"It's completely outlandish, and I think that the stakeholders who are responsible for this behavior have underestimated the blowback from the international community," said Dave Welsh, country director for the labor rights group Solidarity Center.
Choung Choungy, an attorney for some of the detainees, said he would file a complaint.
All the defendants are charged with intentional violence with aggravating circumstances and intentional damage with aggravating circumstances, offenses that could net them up to five years in prison and fines of $1,000 to $2,000.
A doctor who examined 20 of the prisoners found some of them had been severely beaten and treated at the military hospital where some were initially detained, which is also a violation, said Pilorge.
During protests last Thursday, witnesses said troops guarding a factory initiated conflict with the protesters. At least four people were killed Friday when security forces opened fire with automatic weapons on protesters at an industrial park.