British Prime Minister Boris Johnson said it appears to him that P&O Ferries has "broken the law" over the controversial sacking of 800 workers.
He told the Commons that the UK government will be "taking action", and encouraged workers to do the same.
His statement came as the company's chief executive issued an apology for the impact of the decision to sack the staff without notice.
Peter Hebblethwaite said he understood the "anger and shock" about the loss of jobs.
His statement came amid continued protests by unions and workers and followed confirmation that he will appear before politicians tomorrow to be questioned about the dismissals.
"I want to say sorry to the people affected and their families for the impact it's had on them, and also to the 2,200 people who still work for P&O and will have been asked a lot of difficult questions about this," the CEO said.
"Over the last week, I've been speaking face-to-face to seafarers and their partners. They've lost their jobs and there is anger and shock and I completely understand," he said.
"We needed fundamental change to make us viable. This was an incredibly difficult decision that we wrestled with but once we knew it was the only way to save the business, we had to act," he said.
"All other routes led to the closure of P&O Ferries. I wish there was another way and I'm sorry," he added.
Peter Hebblethwaite will appear before a joint hearing of the UK's Transport and Business, Energy and Industrial Strategy committees tomorrow.
Protests were held in Dover and Liverpool today against the sackings, which have been widely condemned by union leaders and politicians.
Huw Merriman and Darren Jones, who chair the committees, said: "This session will aim to understand the detail of the options available to the 800 workers who were roundly dismissed by P&O Ferries last week".
"The cruel nature of their dismissal put employment practices and UK plc under the microscope," they said.
"From P&O Ferries, our members want to know why this action has been taken and how it can be justified. From the Government and its agencies, we want confirmation that our laws are not being broken and safety is not being compromised on our ships," they said.
"This shocking story has raised questions about UK employment law, safety practices, the support of this business through a pandemic and the redress available. We intend to hear from the key players about what they are going to do that means these workers are not left high and dry," they added.
Rail, Maritime and Transport union general secretary Mick Lynch said: "Under pressure from Keir Starmer, the Prime Minister said that P&O Ferries had broken the law by failing to give the Government adequate notice of the redundancies - he has in effect called P&O Ferries liars, as the company said earlier today they have not broken the law".
"But while the PM said they are taking P&O to court, in the same breath he refused Keir Starmer's demand of economic sanctions against P&O owners DP World to enforce the reinstatement of P&O workers," Mick Lynch said.
"It is DP World that have given the instructions to make the mass sackings and break the law, so it is appalling that the Government is scared to take action against DP World," he said.
"Of course P&O need to be taken to court but that by itself won't get our members' jobs back. We need emergency action and legislation if necessary to enforce the reinstatement of our members," he added.
Mr Lynch described the P&O statement as a "half-hearted apology" and again urged the company to reverse the sackings and reinstate the workers.
P&O Ferries operated four routes: Dover to Calais; Hull to Rotterdam; Liverpool to Dublin; and Cairnryan in Scotland to Larne in Northern Ireland.
Sailings between Hull and Zeebrugge, Belgium, were axed in January 2021.
It has almost 4,000 employees and operates more than 30,000 sailings a year.
Around six people who work for the company at Dublin Port have been given assurances that their jobs will be unaffected.
