Calais port mamangement confirmed the interruption of marine traffic.
"There are 400 of us divided between the port and the entrance of the Channel Tunnel and we have nothing to lose," union leader Eric Vercoutre said. "We are demanding that the government obliges the managing director of Eurotunnel to honour his word."
Jacques Gounon, the managing director of Eurotunnel, decided to cede two of the three ferries used by MyFerryLink to its Danish competitor DFDS, provoking the anger of its employees, part of a workers' cooperative.
Unions have taken legal action to win the boats back.
The company, MyFerryLink, was launched in 2012 with boats purchased by Eurotunnel from another company, SeaFrance, which was undergoing liquidation.
It employs around 600 people.
The leaders of the co-op propose, through a public-private partnership, to provide an equivalent service and are supported by local authorities.
"We want our case to be looked at," said Vercoutre, "We've been betrayed but we're determined."