Employees of MyFerryLink, recently sold by Eurotunnel, renewed a blockade of the northern French port of Calais on Monday after a court rejected their bid to extend the service's charter contract with Eurotunnel.
Access to ships was not possible in the afternoon, said union and port sources.
Strike action by around 400 workers last week led to major traffic jams of trucks, prompting migrants around the port to try to stow away on trucks bound for Britain.
Eurotunnel, the operator of the undersea rail link between England and France, in June agreed to sell its Calais-to-Dover ferry business to Denmark's DFDS to end a lengthy battle with British competition authorities.
SCOP Sea France, the co-operative of workers that runs the ferries, asked a commercial court in Boulogne-sur-Mer to extend its contract with Eurotunnel and prevent it from being dissolved after the sale. The court on Monday rejected that request.
DFDS, which is set to take over operation of the ferries on July 2, has pledged to keep 202 out of 577 workers, a level the union sees as unacceptable.
The ferry workers had initially tried to buy the business of operating the two ferries from Eurotunnel themselves but failed.
The French government said it was following the Eurotunnel divestment closely and acknowledged the court's decision.
"Nevertheless, the decision does not absolve Eurotunnel from the obligation to continue to negotiate (with the ferry workers) with the aim of finding an acceptable solution with regard to the jobs affected," said the economy and transport ministers in a joint statement.
For its part, Eurotunnel said in a statement that the only way to preserve jobs on the ferries was for SCOP Sea France's representatives to negotiate directly with the current owner, namely DFDS.