The decision by P&O Ferries to sack 800 seafarers with no notice and replace them with cheaper agency workers has raised safety fears.
Trade union Nautilus International, which represents some of those fired, has urged the Maritime and Coastguard Agency (MCA) to "make sure the ships are safe" as the new crews are "unfamiliar" with the vessels and routes.
P&O Ferries told passengers sailings will be suspended "for the next few days".
