Almost 30 ports were “temporarily dysfunctional” while the port of Marseilles, France's largest, “ground to a halt” as “cargo traffic was paralyzed”, the Associated Press reported.
A spokeswoman for Marseilles' port authority told Bloomberg that the Fos-Lavera terminals were shut down, leaving 67 vessels, including 39 tankers, stranded at the harbour's entrance.
France's largest container port, Le Havre, also faced congestion; while elsewhere in France, protesters blocked access to the Atlantic cargo terminals at Bordeaux, La Rochelle and Saint-Nazaire, and Rouen on the Channel.
Some 300 demonstrators also reportedly blocked access to France's biggest wood terminal in Nantes with a barrage of breeze blocks and burning tires.
France's main union for port workers has called for weekly 24-hour strikes to protest against government reforms and proposed privatisation.
The Confédération Générale du Travail (CGT) has been protesting government plans to reform the nation's ports. At the core of the reforms is the privatisation of cargo handling and terminal operations.
A series of strikes have been staged since French Prime Minister Francois Fillon said in January that cargo handling operations at seven of the country's nine public ports were on course for privatisation.
President Nicolas Sarkozy has backed the reforms, saying he wants to make the ports more competitive.
But the CGT has written to Sarkozy saying there was “no real economic and financial necessity” for the privatisation plans.
"We will increase our protests until we see positive changes in the government's plan," Brice Triboulet, a union representative for the CGT in Le Havre, said.
The bill calling for the port reforms is slated to go before parliament next month.