Thousands of people converged on Piraeus, the port that serves Athens, today to protest against the use of a junta-era law to force ferry workers back to work after a week-long strike.
And the country's two main unions declared a regional strike in Athens for the day in solidarity with the ferry workers.
That hit all public services and included a four-hour walkout by public transport workers.
Ferries set sail for the Greek islands for the first time in a week after the government used emergency powers to break the workers's strike.
Protesters gathered at the port from dawn, while riot police cordoned off the Merchant Marine Ministry to stop thousands of demonstrators reaching the building.
It was the second time in two weeks that the three-party coalition had used the civil mobilisation order to break a strike.
Ministers used it to force rail staff back to work in January after an eight-day strike.
"The government must know that the systematic undermining of union and labour laws violate the country's constitution and international and European agreements that protect workers' rights," civil servants' union ADEDY warned.
It branded it an "anti-democratic practice of criminalising labour and strike action."
The workers are demanding more than six months' worth of arrears in pay and collective work deals with ferry firms.