Nicola Sturgeon has condemned ferry operator P&O’s decision to sack 800 seafarers and replace them with cheaper agency workers after claiming it is “not a viable business” in its current state.

The firm, bought by Dubai-based logistics giant DP World in 2019, said it has suspended sailings “for the next few days”, including its route between Scotland and Northern Ireland.

On Twitter, the Scottish First Minister said: “I’m deeply concerned at P&O announcement – due to the importance to Scotland of Cairnryan/Larne route obviously, but also the impact on 100s of workers.

“Fire & rehire is an appalling practice & offends the basic principle of fair work.”

Workers on board ships have been instructed by unions not to leave.

Coaches carrying agency workers hired to replace them are parked near ships at ports.

Scottish Labour leader Anas Sarwar described the company’s actions as a “devastating decision for all the staff, their families and their communities, and an attack on trade unions”.

He added: “Ferry workers were on the frontline through the pandemic, keeping essential services going – and this is how they are being repaid.

“This will cost vital jobs, plunging people into unemployment in the midst of a cost of living crisis, and it will undermine pay and conditions for years to come.

“This cannot be allowed to stand. We need urgent and united action from the Scottish and UK government to put a stop to this and protect workers’ livelihoods.”

Scottish Green MSP Ross Greer said: “The RMT union has rightly opposed this action in the strongest possible terms and the Scottish Greens support their efforts to save their members’ jobs, including by remaining on their vessels until this is resolved.

“On behalf of the Scottish Green Party, I offer the workers and their unions our solidarity and urge both the Scottish and UK governments to engage with the company and unions as a matter of urgency.”

Scottish Liberal Democracy economy spokesman Willie Rennie said it is “completely unacceptable for P&O workers to be sacked and replaced with foreign agency labour”.

He added: “The First Minister must speak with P&O and make clear that such action will be met with hostility from this Government.”

Finlay Carson, the Scottish Conservative MSP for Galloway and West Dumfries which includes Cairnryan, said the redundancies are “devastating for the workers affected and are likely to have a huge impact in the local community”.

He added: “Reports that staff members were sacked in a pre-recorded video message demonstrate a shocking callousness if true.

“Not only that, but any disruption to crossings would have a hugely damaging effect on trade across Scotland – and of course in Northern Ireland.

“It appears that the UK Government is set to hold talks with P&O – and I sincerely hope that we can reach a satisfying resolution to the situation as quickly as possible.”

P&O Ferries said in a statement: “In its current state, P&O Ferries is not a viable business.

“We have made a £100 million loss year on year, which has been covered by our parent DP World. This is not sustainable.

“Our survival is dependent on making swift and significant changes now. Without these changes there is no future for P&O Ferries.”

The company added that after “seriously considering all the available options”, it has taken the “very difficult but necessary decision” to hand immediate severance notices to 800 seafarers.

UK Transport Secretary Grant Shapps said his officials “will be having urgent discussions with P&O about the situation, particularly of concern for their workers”.