He told the Commons 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 he will appear before MPs on Thursday to be questioned about the dismissals.
He said: “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.
“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.
“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.
“All other routes led to the closure of P&O Ferries. I wish there was another way and I’m sorry.”
Mr Hebblethwaite will appear before a joint hearing of the transport and business, energy and industrial strategy committees on Thursday.
Protests were held in Dover and Liverpool on Wednesday 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.
“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.”
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 falling 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.”
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.
Nautilus said in a statement: “Our members deserve decent employment with decent employers and our work, which has been ongoing for over 165 years, will continue to this end.
“However, P&O Ferries have sunk themselves legally and reputationally. They broke the law, and no end of legal tautology will change that.
“Nautilus International now expects the Government to take all possible action against these law breakers, who think they can buy silence and bully seafarers into unemployment or accepting lower wages and detrimental and unsafe terms and conditions of employment.”