French ferry workers have said they will stop the Irish Ferries ship the Normandy docking at French ports.
It follows a breakdown in talks between Irish Ferries management and unions in Dublin.
Unions are unhappy that the company is no longer employing unionized labour and has recruited lower-paid workers from new EU countries in Eastern Europe.
SIPTU Spokesperson Paul Smyth said: "The French are really saying we're not allowing this cancer of exploiting workers on ferries to spread to ferries in our country".
He said that the embargo of the Normandy earlier this week had been lifted only after SIPTU had pleaded with the French unions.