Thousands of Bombardier jobs in the UK are at risk after the US Department of Commerce ruled against the aerospace firm in a dispute with rival Boeing.
An interim tariff of 220% has been proposed on the import of Bombardier’s C-Series jet to the US.
Boeing had complained Bombardier got unfair state subsidies from the UK and Canada, helping it win a major order.
Bombardier, which is one of Northern Ireland employers, called the ruling “absurd”.
The Canadian firm said Boeing was seeking to use US trade laws “to stifle competition”.
The UK Government and trade unions fear it might even make Bombardier question remaining in Northern Ireland, where it employs 4,100 people in four locations.
About 1,000 jobs are linked to the C-Series, the wings of which are made at a purpose-built £520m factory at Queen’s Island in Belfast.
The programme is not just important to Bombardier jobs in Belfast, but also 15 smaller aerospace firms in NI – and dozens more across the UK – which make components for the wings.
The ruling could potentially jeopardise a major order made last year from US airline Delta – a $ 5.6bn (£4.15bn) deal for up to 125 of the jets.
Bombardier said the decision was “divorced from the reality about the financing of multibillion dollar aircraft programmes”.
What next for Bombardier?
Julian O’Neill, Northern Ireland Business Correspondent
The outcome was predicted – but not the severity of the penalty which triples the cost of a C-Series aircraft sold into the United States.]
The tariff could triple the cost of C-Series aircraft in the US, effectively killing the market for Bombardier.
It also puts a major order with Delta Airlines at risk.
And things could get worse before they get better.
Washington’s Department of Commerce is due to make a second tariff ruling on 5 October.
But a more important date is next February when the US International Trade Commission will either uphold the penalty or remove it.
This was always the focus for Bombardier and its allies.
This dispute has yet to play out and as a consequence it is too early to know the job implications for Northern Ireland with any certainty.
But developments will not lessen the anxiety of workers.
The firm said it had created a “superior aircraft” that is more efficient and comfortable but Boeing was trying to prevent “US passengers from realising these benefits, irrespective of the harm that it would cause to the US aerospace industry and the cost to airlines and consumers”.
But Boeing said the dispute was about “maintaining a level playing field”, and said its aim was to make sure that “aerospace companies abide by trade agreements”.
A UK government spokesperson from the Department for Business, Energy and Industrial Strategy said they were disappointed in the outcome, but emphasised it was “only the first step in the process”.
“Boeing’s position in this case is unjustified and frankly not what we would expect of a long-term partner to the UK – as well as damaging the wider global aerospace industry,” they added.
Jimmy Kelly, regional secretary of the Unite union, said the decision to impose a tariff posed a “direct and very serious threat” to Bombardier jobs in Belfast, as well as many more that are dependent on the company.
Bombardier – which bought Short Brothers in 1989 – is one of Northern Ireland’s largest employers.
The Northern Ireland Executive and UK Government pledged to invest almost £135m in the establishment of the C-Series manufacturing site.
The programme received £750m from Quebec’s provincial government in 2015 when its fortunes appeared to be ailing.