Greek transport systems have been disrupted and schools and tax offices shut after public sector workers walked off the job in protest at new austerity measures and lay-offs demanded by foreign lenders.
The 24-hour strike is the latest in a series of protests since September against a package of wage cuts and tax hikes demanded by Greece's European Union and International Monetory Fund lenders as the price for bailout loans to keep the country afloat.
The measures, which include earmarking 27,000 civil servants for eventual dismissal, remain unpopular among Greeks who say society is crumbling under the weight of spending cuts and tax hikes that hurt mostly the middle class.
'Enough is enough'
On Wednesday, striking teachers, doctors and municipal workers started gathering in central Athens as part of the walkout called by the ADEDY union, which represents about half a million public sector workers or roughly a quarter of the country's workforce.
"We want to tell the government enough is enough! Enough with layoffs, wage and pension cuts, the collapse of the public sector, enough with these tax hikes," said Adedy unionist Despina Spanou.
Greece's other major union, the private sector union GSEE, said it would hold a three-hour stoppage in solidarity and join the march through the streets of central Athens.
The Communist-affiliated PAME group was expected to hold a separate rally.
Some domestic flights were grounded and about 100 workers occupied the headquarters of Athens' city train company on Wednesday in protest at planned wage cuts.
Train workers also started a 48-hour strike against the conservative-led coalition's plans to privatise Greece's national railways.
Metro and tram workers walked off the job for a few hours on Wednesday and plan a 24-hour strike on Thursday.
Thousands were expected to march to the administrative reform ministry which oversees public sector reform, however unionists expected a smaller turnout that previous strikes.
Unions said that some Greeks, although fed up with austerity, could no longer afford to lose a day's wages.
Police deployed about 2,000 officers in central Athens.