Fears are growing for the jobs of thousands of UK workers who provided baggage handling and other services for Flybe following the airline's collapse.
Thousands of employees at ground handling firm Swissport, based at regional airports across the UK, are anxiously waiting for news.
Workers include baggage handlers, check-in staff and engineers.
Some engineers were told late on Wednesday that they were being laid off, sources said.
Nadine Houghton, GMB national officer, said: "The collapse of Flybe is a tragedy for the company's loyal workforce.
"A domino effect now puts 1,400 jobs in the wider supply chain at immediate risk and threatens the future of vital regional airports."
Brian Strutton, general secretary of the British Airline Pilots' Association (Balpa), said: "Some 2,000 staff members have woken up to the loss of their jobs, and many thousands more airport and other workers in the supply chain will also be deeply concerned.
"I believe there is a good economic case for a strong regional UK airline. Flybe operated routes which were not only economically and regionally vital, but also profitable.
"We will be exploring with the administrators which parts of Flybe can be rescued or sold as a going concern in the hope that as many jobs as possible can be saved."
The GMB said thousands of Swissport baggage handling jobs are at risk at Birmingham, East Midlands, Cardiff, Aberdeen, Edinburgh and Manchester airports following the collapse.
Ms Houghton said: "The Government needs to urgently step in with a rescue plan for our regional airports to minimise damage and protect livelihoods. This means doing the right thing now and not prevaricating behind state aid rules nonsense that can be dealt with in due course. The UK economy and workforce must come first."
The GMB warned that up to eight regional airports face closure in the wake of the Flybe collapse, directly employing at least 1,000 workers in total.
The airports, including Anglesey, Southampton, Belfast, Exeter, Newquay, Wick and Jersey, are deemed at risk because more than 50% of their scheduled departures in 2019 were Flybe aircraft, said the union.
On Thursday, the Government defended its decision not to save Flybe from collapse, and said it "stands ready" to support the failed airlines' passengers and staff.
Transport Minister Kelly Tolhurst said the Government had been "working tirelessly" to help the business stay flying, but the spread of Covid-19 has hampered these efforts.
In a statement, she told MPs: "Unfortunately, in a competitive market, companies do fail and it is not the role of Government to prop them up." She added: "We have been working tirelessly to explore multiple options with Flybe's shareholders to find a solution.
"Flybe outlined that problems with their business had been compounded by the outbreak of coronavirus which in the last few days had resulted in a significant impact on demand.
"The directors, therefore, decided it was not viable to keep Flybe operating."
Ms Tolhurst said there is "sufficient capacity" with other airlines to help passengers stranded abroad return home.
She told MPs: "Given the time of the year, the nature of Flybe's business and fleet, and the routes it flies - sufficient alternative transport routes should be available either with other airlines or by road and rail.
"The number of passengers abroad is small and it is further reduced as a result of coronavirus. For those passengers who are abroad, there is sufficient capacity on commercial airlines to return to the UK.
"The Civil Aviation Authority and the Secretary of State are encouraging these airlines to offer rescue fares and this is already happening."