Prime Minister Theresa May has hit back at the US decision to impose tariffs on Bombardier, saying she was "bitterly disappointed" by the move, as concerns grow over thousands of UK jobs.
She said the government "will continue to work with the company to protect vital jobs for Northern Ireland".
America's Department of Commerce announced yesterday it had made a preliminary finding that the Canadian firm had received unfair state subsidies and sold its CSeries jet below cost.
It has now imposed an interim tariff of 219.63 per cent on the company's new commercial jets to the US.
While Boeing said the dispute was about "maintaining a level playing field and ensuring that aerospace companies abide by trade agreements", Bombardier, which is one of Northern Ireland's largest employers, has branded the ruling "absurd".
A government spokesperson said:
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.
"This is a disappointing interim statement, but only the first step in the process," they added. "We will continue to work closely with the Canadian government to encourage all parties to reach a credible resolution as quickly as possible."
Trade unions have expressed concerns that tariffs could make the company question whether to stay in Northern Ireland, where it employs over 4,000 people.
The effect could be wider too, as Bombardier in Belfast has an overall supply chain of around 800 firms in the UK and Ireland, according to trade body ADS.
Meanwhile, the Confederation of British Industry (CBI) warned the decision represented a challenge to the Northern Ireland economy.
CBI Northern Ireland director Angela McGowan, said: "Bombardier makes a huge contribution to the Northern Irish economy. They are a major regional employer and support a wider supply chain that stretches across Northern Ireland."
She added: "The decision by the US Department of Commerce represents a challenge to the Northern Ireland economy and places an important driver of regional economic growth at risk."
Paul Everitt, the boss of trade body ADS, said the ruling was "extremely disappointing and unsettling for Northern Ireland's aerospace industry", but added that there was still a long way to go in the process.
He said: “Bombardier is an important part of the UK aerospace industry, and especially in Northern Ireland where it employs thousands of people. The company has high potential for future growth as demand for new aircraft remains high.”
The possibility of the UK taking a stand in terms of procurement cuts has been raised, but aerospace analyst Howard Wheeldon said this would be seen as "merely political posturing".
He said: "Threats by both the Canadian and British Prime Ministers to halt purchase of Boeing military planes unless the dispute can be sorted out are hardly conducive to finding a satisfactory way out of the current impasse. They are as pointless as they are seen by most as merely political posturing."
The US International Trade Commission will consider the case ahead of a final ruling in February.