Two of the competitors of P&O Ferries are going to meet with officials from the Department for Transport to discuss the situation.
The government plans to force ferries to pay the minimum wage in UK waters, so bosses from Stena Lines and DFDS have been invited for talks on Monday.
P&O Ferries replaced staff with agency workers who were paid less than the minimum wage.
The prime minister supports calls for the P&O Ferries boss to step down.
The decision to sack 800 workers without notice broke the law, according to P&O Ferries boss Peter Hebblethwaite.
The unions held demonstrations at several ports on Saturday.
The European Causeway, a P&O Ferries vessel, was taken into custody by authorities.
The ship was held in Larne because of failures on crew familiarisation, vessel documentation and crew training, according to theMCA. P&O Ferries said it would make changes to return the ship to service.
After P&O replaced their members with agency workers whose average hourly rate of pay would be less than the UK minimum wage, unions raised fears over a lack of training of new crew.
The minimum hourly rate in the UK does not apply to the company's ships that operate internationally.
P&O Ferries said it had to replace crews because it was losing 100 million dollars a year and would not be a viable business without the changes.
Grant Shapps is expected to propose measures this week that will force ferry companies to pay the minimum wage in the UK.
If P&O ships are unable to sail, there will be concern over the Easter holiday travel plans.
A Department for Transport spokesman said: "Ministers are working to understand how we can ensure the continuation of services in collaboration with other operators."