Officials said they were looking for two more suspects in the shootings Wednesday, reportedly related to a dispute concerning back pay, ekathimerini.com reported Thursday.
The incident occurred when about 200 workers allegedly demanded six months of unpaid wages from their employer, officials said. The workers began arguing with three Greek supervisors, and at least one supervisor fired at the migrants with a shotgun.
Local reports said as many as 30 workers were injured, with several of them said to be in a critical condition Wednesday night, ekathimerini.com said.
The leftist Syriza opposition coalition, in a statement issued Wednesday, called the incident a "criminal, racist act."
Greece's Communist Party Thursday criticized the "modern-day slave trade and the inhuman labor conditions of migrant workers," saying it was "synonymous with ... capitalism."