The government has been criticised for allowing increasing numbers of foreign workers on British ships in the wake of the MSC Napoli disaster off the Dorset coast.
It has emerged that at least six nationalities were represented among the 26-strong crew of the doomed containership.
All employees have now been evacuated from the breached vessel, which took on water after a hole was punched in its starboard side.
"We need a full investigation into the causes of this accident, and to focus our long-standing concerns about the way in which British ships are now being crewed," said Nautilus UK general secretary Brian Orrell.
Unions have long argued that safety at sea relies on a common language among crew members.