Another P&O Ferries ship has been detained casting doubt on the firm's Dover (England) operations restarting before Easter.
The MCA (Maritime and Coastguard Agency) said inspectors had found a "number of deficiencies".
The Spirit of Britain ferry, which normally serves the Dover (England)-Calais (France) route, can't set sail until the issues have been addressed.
P&O Ferries said it looked forward to welcoming clients again as soon as mandatory safety tests had been passed.
The company faced criticism after the no-notice sacking of 786 P&O employees. P&O Ferries faces criminal/civil investigations into the circumstances around the redundancies.
The MCA said they had advised P&O to invite them back once they had addressed the issues.
P&O Ferries' Dover-Calais routes are now suspended. The company said it would not restart services on the route before Friday at the earliest.
The Maritime and Coastguard Agency has been making its way through inspections of 8 vessels of P&O Ferries to ensure they are fit to sail. European Causeway and Pride of Hull have been inspected and cleared to sail, while Pride of Kent, which normally sails on the Dover-Calais route, remained under detention with Spirit of Britain.