Ferries between Larne and Cairnryan remain suspended after P&O sacked 800 of its workers last week.
The company confirmed the suspension on Monday morning saying it is "no longer possible to arrange travel via an alternative operator on this route".
And their advice to customers was to "seek alternatives themselves".
Read more: P&O workers at Larne Harbour living a 'bad dream' after shock redundancies
Union representatives are set to brief a Stormont committee on its plans to launch a legal challenge against the ferry giant.
Ulster Unionist Mike Nesbitt said unions will be given the opportunity to “vent their anger” against the “Orwellian” treatment of P&O workers.
Mr Nesbitt also said Stormont does not have the legislative power to compel senior management at P&O to appear before a committee before the Assembly dissolves.
The ferry operator, bought by Dubai-based logistics giant DP World in 2019, has insisted the decision to cut jobs was “very difficult but necessary” as it was “not a viable business” in its current state.
Workers staged a protest at the P&O terminal in Larne Port on Friday afternoon, and spoke out following their ordeal.
Daniel McDonald had been working at P&O Ferries for 17 years, and until Thursday had been an Assistant Manager on the European Causeway.
The 45-year-old works on a two weeks on, two weeks off basis, and was onboard starting his shift as normal at 8am. However, he was soon informed by a colleague that the ship would not be sailing that day.
"I wondered if there was an engine problem, and they said they didn't know, but all the cars were being sent away. Usually if there's a delay, the cars would stay," Daniel told Belfast Live.
"We were told by the captain there would be an announcement made from senior management, and he said he didn't know what was going on. He was just told all P&O ships aren't to sail until further notice.
"Then your mind starts thinking - Have we all lost our jobs? Have they gone bust? You think the worst case scenario, but what was ahead of us we definitely didn't expect."
Read more: RECAP as P&O Ferries cancels services with 800 workers fired
Read more: P&O Ferries issues statement amid ongoing delays at ports
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