Thousands of striking truck drivers have been lining the highways since Monday to protest against plans to open the sector to competition, a key reform in a multi-billion dollar EU/IMF package aimed at pulling Greece out of a debt crisis.
Fuel has run out in all but a few of the capital's petrol stations and shortages are already reported in many major cities.
The truckers say that opening the freight sector by reducing new licence charges is unfair to existing operators who have already paid high start-up fees running up to $390,000.
"The state sold us these licences, so the state should compensate us," George Tsamos, the head of the truckers' union, told Flash Radio.
Barnaby Phillips, Al Jazeera's correspondent in Athens, said: "[The] truck drivers are furious about government attempts to liberalise their profession.
"They say that in some case they paid tens of thousands of euros for their licences and if their profession is opened up to anyone, their livelihoods will be destroyed.
"They've been on strike for three days now and [the] strike has had a big impact on Greece ... here in Athens for example, 80 per cent of petrol stations have now run out of fuel.
"For its part, the government is showing a much firmer hand than it has in the past ... it has declared the strike illegal.
"It's ordering the people to go back to work, it says the liberalisation of the economy is essential if there is to be economic progress in Greece."
The drivers say they will not directly defy the emergency order, but will continue their protest with various forms of disobedience.