Trade unions in Greece have called the first general strike since the conservative-led coalition government came to power in June.
Wednesday's 24-hour walkout is to protest at new planned spending cuts of more than 11.5bn euros ($15bn; £9bn).
The savings are a pre-condition to Greece receiving its next tranche of bailout funds, without which the country could face bankruptcy in weeks.
Large anti-austerity demonstrations are also planned.
Greece needs the next 31bn-euro instalment of its international bailout, but with record unemployment and a third of Greeks pushed below the poverty line, there is strong resistance to further cuts.
The government of conservative Prime Minister Antonis Samaras is also proposing to slash pensions and raise the retirement age to 67.
Fears of violence
Workers from a diverse range of sectors are taking part in the strike, from doctors to air traffic controllers.
It was called by the country's two biggest unions, which between them represent half the workforce.
A survey conducted by the MRB polling agency last week found that more than 90% of Greeks believed the planned cuts were unfair and a burden on the poor.
The BBC's Mark Lowen in Athens says that, with demonstrations planned, many people fear a repeat of the violence that has hit the streets in previous protests.
Thousands of police have been deployed in the centre of Athens to prevent a flare-up.
Greece is currently trying to qualify for the next instalment of its 130bn-euro bailout, which is backed by the IMF and the other 16 euro nations.
The country was given a 110bn-euro package in May 2010 and a further 130bn euros in October 2011, but correspondents say its neighbours are reluctant to stump up more money.
Greece needs the next tranche of its bailout to make repayments on its debt burden. A default could result in the country leaving the euro.