Strikers at France’s top oil port have been meeting unions from nearby refineries over possible joint action.
That raised the prospect of a halt to production at several large plants and a further jump in fuel prices.
Currently 30 ships with crude and oil products are blocked at the Fos-sur-mere/Lavera terminal near the Mediterranean port of Marseille.
The strike, which is over job guarantees during a reorganisation at the port, entered its tenth day on Wednesday.
The industrial dispute has already trimmed fuel output at six refineries in France, pushing up European benchmark gasoline barge prices.
The plants served by the port can process over one million barrels per day, that is around seven percent of Europe’s total capacity.