A strike stopped ferry services to the Greek islands and disrupted public transport in the capital Athens ahead of May Day protests Wednesday against Greece's prolonged economic austerity policies.
Ferry services were expected to be halted the entire day as the Panhellenic Seamens' Union took part in the general strike called for by the country's two main unions.
Public transport in the capital returned to normal around 9 am (0600 GMT) after early work stoppages in the metro and bus services.
But police have demanded that four metro stations in the city centre remain closed, because of rallies due to start at 0800 GMT.
"May 1st, day of memory, honour and struggle" was the call of private sector union GSEE, which along with public sector union ADEDY, is organising the protest.
Communist-affiliated group Pame is also scheduled to hold its own march in the Athens city centre.
Many shops have remained open however, as the government recently decided to relocate the May 1 public holiday to May 7, because of the celebration of Orthodox Easter on May 5.
The government's decision, an attempt to help traders maximise sales during the Orthodox Holy Week, is likely to affect protest turnout.
The heavily-indebted country has adopted a strict austerity programme, in return for vital rescue loans from its international creditors.
On Sunday the government voted to adopt a law that will allow the dismissal of 15,000 civil servants as part of the terms set by the European Union and International Monetary Fund (IMF).
The unions had organised a protest outside the parliament at the time of the vote, but their call was only met by around 800 people.
Since 2010, the EU and IMF have committed a total of 240 billion euros ($316 billion) in rescue loans to Greece.