Greek public sector workers walked off the job on Wednesday in protest at new austerity measures and planned layoffs, disrupting local transport, grounding flights and shutting schools and tax offices.
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 international lenders as the price for bailout loans to keep the country afloat.
The walkout was called by the ADEDY union which represents about half a million public sector workers or about a quarter of the country's workforce.
"We demand that the government changes these unjust policies that hurt workers and kill the public sector," said ADEDY chief Costas Tsikrikas. "We expect a large turnout in the strike."
Thousands of teachers, doctors and municipal workers were expected to take to the streets and rally in central Athens around midday, though turnout may be smaller than protests last month before the austerity package was passed in parliament.
The measures - which include earmarking 27,000 civil servants for eventual dismissal - remain deeply unpopular among Greeks who say society is crumbling under the weight of spending cuts and tax hikes that hurt mostly the middle incomes.
But the rallies have lost some of the momentum since the austerity bill was approved and Athens received long-delayed funds from the European Commission, European Central Bank and International Monetary Fund, averting the risk of bankruptcy.
Greece's other major union, the private sector union GSEE, said it would hold a three-hour stoppage in solidarity and join the march to the administrative reform ministry. The Communist-affiliated PAME group was expected to hold a separate rally.
Train workers also started a 48-hour strike against the conservative-led coalition's plans to privatise Greece's railway company. Metro and tram workers will walk off the job for a few hours on Wednesday and plan a 24-hour strike on Thursday.
Police deployed about 2,000 officers in Athens on Wednesday, but police officials said they did not expect serious violence.
Major protests in Athens are often marked by small-scale clashes between groups of hooded protesters who hurl stones and petrol bombs at riot police who in turn respond with teargas.
The government has implored Greeks to endure the cuts and promised they will be the last. But that has convinced few in a nation where unemployment has topped 26 percent and poverty levels have soared.
"We want measures that create growth and boost employment, we want the government to crack down on tax evasion instead," Tsikrikas said. "We will keep protesting."