Hospitals, transport services and government offices across Greece have been severely affected by a general strike over new austerity measures.
Industrial action began on Tuesday but has now been ramped up nationally by members of the big trade unions.
Ferry services and buses have been halted and air-traffic controllers will stop work for four hours.
MPs are set to vote on controversial reforms on Thursday that will cut pensions and end tax breaks.
The left-wing Syriza government needs to make further savings before eurozone finance ministers agree to hand over further loan cash as part of its latest bailout deal.
The new measures will not come into force until 2019 and 2020 but Prime Minister Alexis Tsipras has to persuade eurozone finance ministers next Monday to provide the next loan instalment of €7.5bn (£6.4bn; $8.2bn).
Greece is facing its next big debt demand in July and has had three bailouts from the EU and IMF so far.
The country has fallen back into recession for the first time since 2012, according to figures that emerged on Tuesday.
Gross domestic product (GDP) fell by 0.1% in the first three months of 2017 after shrinking by 1.2% in the final quarter of last year.