British Airways is set to make up to 12,000 workers redundant, the firm's parent company IAG has said.
The airline, which employs 42,000 people, has been hit hard by the coronavirus pandemic which has caused a global collapse in passenger numbers.
The move to lay off staff will potentially include ground staff, cabin crew and pilots.
It comes as the airline continues to run a "limited" service for essential flights, with plans to restart flights to Tel Aviv next month.
In a statement, IAG said: "In light of the impact of Covid-19 on current operations and the expectation that the recovery of passenger demand to 2019 levels will take several years, British Airways is formally notifying its trade unions about a proposed restructuring and redundancy programme.
"The proposals remain subject to consultation but it is likely that they will affect most of British Airways' employees and may result in the redundancy of up to 12,000 of them.
"As previously announced, British Airways has availed itself of the UK's Covid-19 job retention scheme and furloughed 22,626 employees in April."
Among the firm's facilities in Wales includes a maintenance depot near Cardiff Airport. The depot, which opened, in 1993, employs around 800 people.
The airline has two additional facilities in south Wales - British Airways Interiors Engineering in Blackwood and British Airways avionic engineering in Pontyclun.
Around 4,500 pilots and 16,000 cabin crew work for BA.
IAG did not provide a breakdown of how many people in each role could be made redundant.
Brian Strutton, general secretary of pilots' union Balpa, said: "BA pilots and all staff are devastated by the announcement of up to 12,000 possible job losses in British Airways.
"This has come as a bolt out of the blue from an airline that said it was wealthy enough to weather the Covid storm and declined any Government support.
"Balpa does not accept that a case has been made for these job losses and we will be fighting to save every single one."
IAG announced the planned job cuts as it revealed that revenues plunged 13% to 4.6 billion euros (£4 billion) in the first three months of 2020 after the pandemic hit capacity.
The group also swung to a 535 million euro (£466.3 million) operating loss before exceptional items, from a 135 million euro (£117 million) profit for the same period last year.
It said profits were hit hard by a 1.3 billion (£1.1 billion) charge for the year after over-hedging on fuel and foreign currency.
Airlines around the world face a struggle to survive due to the pandemic.
Sir Richard Branson has warned that Virgin Atlantic will collapse unless it receives Government support.
It emerged on Monday that most of Norwegian's aircraft will remain grounded for a year.
