Greek unions started a 48-hour strike on Tuesday ahead of a planned parlimentary vote on further austerity measures this Wednesday.
The latest stoppage will see wide sections of the economy grind to a halt. Civil servants, air traffic controllers and transport workers amongst others will down tools.
If MPs do not back the new spending cuts, Greece's international lenders could withhold a 31.5-billion-euro installment of bailout aid.
Antonis, a striking security guard, said: "What we demand is that our deputies won't dare to vote 'yes' on these measures. If they do, as I look you in the eyes and with full awareness of what I am saying, there will be extreme forms of social explosion."
Proposals include a fifth consecutive cut to pensions, hiking the retirement age and slashing wages.
The Greek government says the measures will save some 13.5 billion euros.