The union organised marches across Greece to celebrate May Day and to protest against the austerity measures and the EU-IMF relief package were marred by incidents of violence in Athens and Thessaloniki.
Police said about 17,000 people joined the Athens marches and around 5,000 in Thessaloniki to vent their anger at the deep budget cuts which are being widely anticipated.
The demonstrators who took to the streets of Athens and Thessaloniki expressed their anger with and opposition to the cutbacks on salaries, raises in taxes, reforms to the pension system and a new package of more harsh measures which are expected to be announced imminently.
During the two separate massive rallies organised by umbrella public sector union ADEDY, private sector counterpart GSEE and labor unions close to the two Left parties in parliament, clashes between young protestors and police were reported at Syntagma square in front of the Greek parliament and at the old University of Athens nearby.
After the protests ended, groups of young hooded people hurled rocks and molotovs at police, who answered with teargas at Exarchia.
Protestors also physically and verbally attacked PASOK MP Apostolos Kaklamanis, after spotting him among pedestrians on the sidelines of the Athens march.