The UK's Maritime & Coastguard Agency (MCA) is having to reassess about 500 seafarers after discrepancies were discovered with a course provider.
The crew in question completed safety-critical courses governed by the requirements of the International Convention on Standards of Training, Certification and Watchkeeping for Seafarers (STCW).
Affected seafarers will be contacted within five working days.
Katy Ware, MCA director of Maritime Safety & Standards, said: "As a flag state, the MCA takes its role very seriously.
