The Acropolis and other ancient sites in Greece are closed to the public after guards called a 24-hour strike over a pay and contract dispute with the government.
Monday's protest was not directly related to Greece's bailout measures, but the country's left-wing government is under renewed international pressure to limit spending and agree with lenders on new austerity measures and reforms.
A union representing the striking workers is seeking additional staff and overtime pay.
A statement said: "We hope these problems, that have no fiscal impact,can be dealt with so that the Easter holidays and tourism season can start without any problems at museums and ancient sites."
The hilltop buildings of the Acropolis overlooking Athens include the Parthenon and the Temple of Athena Nike.