The RMT union has written to Shipping Minister Kelly Tolhurst calling for "dynamic" government action to help save more than 1,000 jobs at P&O Ferries.
The ferry operator, based in Dover, Kent, said earlier this month that the reduced number of vessels and downturn in business had forced its decision to lay off staff.
In his letter, RMT general secretary Mick Cash called on the UK government to take a number of steps to save jobs at the firm and to re-build UK seafarer employment.
Among the government steps called for by Mr Cash included a call for a public statement opposing compulsory redundancies.
In addition, Mr Cash urged the government to press P&O Ferries to use the extended furlough scheme in the UK.
Mr Cash said: “We have a healthy dialogue with the Shipping Minister and her officials but we must now see dynamic action from the government in support of British seafarers jobs on vital ferry routes that are being subsidised by the taxpayer.”
The owners of P&O Ferries had previously stated the business needed £257m in aid to avoid collapse.
P&O has said a consultation period was under way and that it was “clear that right-sizing the business is necessary to create a viable and sustainable P&O Ferries to get through Covid-19".