The Greek government has no funding left for public sector wages - usually paid in the middle and at the end of each month. It has ordered the public authorities to hand over all spare cash to the central bank.
The government has the option of paying civil servants in IOUs or a parallel currency for a while, but these are likely to prove insufficient given the state of Greece's banks.
Analysts say the social unrest that could result from this might trigger a Greek exit from the euro zone.
Real wages per worker in Greece were about 17 per cent lower last year than in 2009.
This was due in part to cuts in minimum wages and civil servants' salaries, both conditions that Greek's creditors imposed as part of austerity measures.
Between 1976 and 2012, the number of civil servants in Greece tripled, while the private sector workforce grew just 25 per cent.