Greek police clashed with striking truck drivers outside an oil refinery near the northern city of Thessaloniki on Friday after unions defied a government order to go back to work.
The country's 33,000 hauliers are protesting against plans to open up the road freight industry to competition - a reform required under a multi-billion euro European Union and International Monetary Fund bailout plan for Greece's debt-laden economy.
Police in full riot gear hit truck drivers with batons to stop them blocking a truck from leaving the refinery. A police official said two protesters were injured.
Truckers said on Friday they would extend a five-day strike that has has disrupted fuel supplies across the country in the busy tourism summer season, leading to long queues at petrol stations and hurting harvests, imports and exports.
Road freight is one of the most closed professions in Greece, with no new licences issued for nearly 40 years.
Those in circulation are sold from person to person for hundreds of thousands of euros.
Fully opening up the country's 70 or so closed professions would boost GDP by 10% in five years, according to an Athens-based think tank.