On Saturday, an anti-fascist group ORMA claimed that affiliates of the Golden Dawn party attacked them in Perama, a suburb of Piraeus.
"We were attacked by Golden Dawn members with crowbars outside of the offices of Saint Nicholas Union," ORMA said, referring to a ship worker union linked to the far-right party, Golden Dawn.
They also said they pushed back the attackers. However, when they went to a police station to file a complaint, ORMA members were arrested, the group said.
In response to the incident, Syriza said in a statement that the "poisons of fascism and racism have no place in Perama or anywhere" else.
On its website, Golden Dawn, which currently has 16 seats in the Greek parliament, dismissed the allegations as "ridiculous".
Saturday's attack follows a reported assault on two Pakistani migrant labourers in an outdoor market in Agioi Anargyroi, who were attacked for no apparent reason whilst working.