A leftist group on Friday blockaded the Greek Finance Ministry, the scene of negotiations on the nation's latest financial rescue, hanging a huge banner covering five storeys of the building in central Athens.
"Organise and fight for an overthrow -- General Strike," read a banner draped by activists from the Communist-affiliated PAME, which advocates non-violent protest.
Talks on funding from the European Union and International Monetary Fund, following Greece's 110 billion-euro bailout a year ago, have been held at different sites.
But the ministry, on Syntagma Square where protesters gather nightly to demonstrate against corruption and economic mismanagement, has been a centre for the month-long negotiations between the Greek government and inspectors from the EU, IMF and European Central Bank.
It was not clear how far the PAME activists had penetrated the building but access was blocked.
"We have a sacred duty to our children and ourselves to cancel plans to turn workers into modern slaves," PAME said in a statement. "We must not allow our children to work for hunger wages. If we do not fight to overthrow these policies their working future will be hell."
Greece is set to impose a deeper bout of austerity and to promise to speed up a privatisation drive in return for a new international bailout to avoid a debt default.
Prime Minister George Papandreou will present on Friday a medium-term budget plan, which a government official said included 6.4 billion Euros in new measures to cut its 2011 budget deficit.
Greece's main public sector union, ADEDY, said it would join its private sector sister union GSEE in a nationwide strike on 15 June.