Up to 287 Swissport workers at the north's two main airports face redundancy, the Unite union has warned.
The company employs 8,500 workers at airports in 48 countries, including baggage handlers and check-in staff.
It told staff on Wednesday that up to 4,556 jobs - more than half its UK workforce - could be cut as a result of the impact on air travel caused by the coronavirus crisis.
In a statement, the union Unite said 175 employees at Belfast City and 112 at Belfast International airports face the immediate prospect of redundancy.
Regional officer George Brash said every single Swissport worker at Belfast City Airport had been issued with a protective notice.
Swissport's chief executive Jason Holt said the company had to reduce the size of its workforce to survive.
The collapse in air travel means its revenue is forecast to be almost 50 per cent lower than last year.
Ground service jobs at the airport have also been under threat since the collapse of Flybe in early March. The regional airline had accoutned for more than 80 per cent of the flights operating from Belfast City Airport.
Unite has said the move is "entirely unnecessary", claiming that the workers could be furloughed for the time being.
"Without baggage handlers, gate staff and security desk workers, the airport cannot operate; the scale of this announcement casts a shadow over the future of both Belfast airports, in particular Belfast City," said Mr Brash.
The union representative also directed sharp criticism at Stormont.
"In March, at the start of the Covid downturn Swissport workers joined with colleagues from the collapsed airline Flybe to rally in front of Stormont to seek urgent intervention but absolutely nothing has happened since.
"In the intervening period, Belfast International has made 45 redundancies and the small operator, Jet2, 34 – while Easyjet has announced 4,500 job-losses across the UK although we haven’t a breakdown of how that affects Northern Ireland. There is a mounting crisis in our aviation sector.
In a message to Swissport staff, Jason Holt said: "We must do this to secure the lifeline of funding from lenders and investors to protect as many jobs as possible in the United Kingdom and Ireland.
"It's true that we've seen tough times before - volcanic cloud, 9/11, the financial crisis - and we've weathered these. But this time it's different. We have never seen anything like Covid-19 in our lifetimes.
"We are now facing a long period of uncertainty and reduced flight numbers, along with significant changes taking place to the way people travel and the way goods move around the world. There is no escaping the fact that the industry is now smaller than it was, and it will remain so for some time to come."
Mr Holt said: "This has been a very difficult decision to make, and I know it will be immeasurably harder for those who will eventually be leaving the company.
"But we must do it, if we are to continue operating and protect as many livelihoods as possible in the long run."
He told staff that Swissport had been hit hard by the Covid-19 outbreak, beginning with the collapse of Flybe in March, adding: "While some areas of the business have been busier than others, across the company revenue has almost been completely lost. As of May, it's down by more than 75 per cent, and we still have bills to pay.
"Our company is a crucial part of the industry triangle made up of airports, airlines and airport services companies, but we operate a low-margin, high-volume business model.
"When aircraft aren't flying our source of revenue evaporates. The unfortunate fact is that there simply aren't enough aircraft flying for our business to continue running as it did before the Covid-19 outbreak, and there won't be again for some time to come. We must adapt to this new reality.
"Although our airline partners are hoping to increase their numbers of flights, they too are struggling to plan schedules and stick to them.
"The International Air Transport Association has forecast that airline industry traffic may not recover to 2019 levels until 2023, and under some scenarios not until 2024."
