Thirty-five anti-austerity protesters, members of the Communist Party-affiliated PAME union, were to face a prosecutor on Thursday in Athens after storming the office of Greece's Labor Minister on Wednesday.
The suspects have been accused with disturbing the peace and damaging public property.
Hundreds of unionists reportedly gathered at the capital's Evelpidon court complex to protest their detention.
On Wednesday, riot police were deployed to remove the demonstrators from the office of Labor Minister Yiannis Vroutsis and 35 people were taken into custody. The union was allegedly protesting comments Vroutsis had made about the social security system.
During the operation, police fired teargas and used batons to disperse roughly 300 demonstrators who rallied outside the ministry in solidarity.
“Violence in any form must be condemned,” government spokesman Simos Kedikoglou said in a statement Wednesday condemning the occupation of the labor minister's office.
“The government will not put up with this kind of incident,” he added.
PAME denied the government’s claims that Labor Ministry offices were damaged during the protest. The union said the damage in the ministry was done by police as a “provocation” against unionists.
In statements Wednesday KKE spokesman Thanassis Pafilis slammed the ministry's “vulgar propaganda” and asked police to release footage taken during the operation.
KKE leader Aleka Papariga returned from a visit to farmers demonstrating in Thessaly to demand the release of those detained. SYRIZA, the main left-wing opposition, also called for their release.
In a related development, Greek Public Order Minister Nikos Dendias on Wednesday said that the conservative-led government would continue its clampdown on crime and law-breaking.
“The law must be enforced for everyone,” Dendias said.
“The country must finally settle its accounts with the post-1974 era,” he said pledging to deal with violence, crime and illegal immigration.