The building is located on the corner of Drosopoulou and Lela Karayianni streets. It was the former residence of Karayianni, who was tortured and executed by Nazi occupying forces in 1944 for her participation in the Bouboulina resistance movement.
The building has become a symbol for radical left-wing groups and has been occupied since April 1988, when it was taken over by a group of university students, making it the oldest squat in Athens.
The building belongs to the University of Athens and the Education Ministry.
The group of squatters in the building has been involved in organizing several anti-racism events in Kypseli, which has a large migrant population, in response to a spike racially-motivated assaults against migrants over the past few months.
Dozens of people gathered outside the building on Tuesday to protest the police operation, shouting slogans of solidarity with the squatters.
Meanwhile, a rally has been planned at 3 p.m. outside Athens police headquarters on Alexandras Avenue to protest the arrests.
Last week, police raided another two squats in central Athens, including the notorious Villa Amalia, which had been reoccupied following a police sweep last month.