Workers from the Skaramangas Shipyards, that dealt mainly with military contacts, were on Thursday protesting outside the National Defense Ministry.
Tensions rose after a group of workers, who are demanding six months backpay, raised the metal barriers at the entrance and reached the courtyard.
Riot police prevented them from entering the building. The standoff continued as workers demanded that they hold a meeting with the minister.
Reports said the minister, Panos Panayiotopoulos, was en route to a celebration commemorating 100 years of the end of the Balkan wars.