The Port of Dover was plunged into chaos on Thursday afternoon after P&O Ferries sacked 800 crew members.
Lorries and passengers were left stranded in check-in lines at the port as employees staged protests, with pictures showing huge queues of cars stuck in gridlock.
The firm sparked fury after announcing that all 800 of its seafarers would be made redundant to stem “unsustainable” financial losses.
The RMT Union instructed staff to stay on board vessels once they were in dock or risk being “locked out” of their jobs.
General secretary Mick Lynch said: “We have instructed our members to remain onboard and are demanding our members across P&O’s UK operations are protected, and that the Secretary of State intervenes to save UK seafarers from the dole queue.”
P&O told customers to use rival operators after suspending its operations.