Prime minister Theresa May told US planemaker Boeing yesterday that it is undermining its commercial relationship with the UK with its conduct in a trade dispute with Canada's Bombardier.
May intervened in the trade dispute between Canada and the US Department of Commerce imposed a preliminary 220-per cent duty on Bombardier's C Series jets in response to a complaint by Boeing.
According to Boeing, Bombardier was receiving unfair state aid from the UK and Canada.
The US ruling has put 4,200 jobs at the plant in the British province of Northern Ireland are at risk. The facility manufactures the carbon wings of the jets.
''We have a long-term partnership with Boeing in various aspects of government and this is not the sort of behaviour we expect from a long-term partner and it undermines that partnership,'' May said in response to a question at a Bank of England event.
Boeing, the world's biggest plane maker, has said it remained committed to the UK.
May's criticism of Boeing is seen as an indication of the importance of the plant to the small Northern Irish political party on which her government has leaned on after she lost her parliamentary majority in June following a botched election campaign.
According to commentators, the UK would however find it difficult to risk its relationship with one its most important defence equipment suppliers.
Canada's Bombardier is one of Northern Ireland's biggest employers and the prospect of job losses there could unhinge the arrangement between the Conservatives' and the Democratic Unionist Party.
May also highlighted a wider issue at the event. "I think there is a real challenge for us globally today, because I think that there are aspects of protectionism creeping in around the world," she added, saying that she wanted the UK to be "a global champion of free trade".
In 2016, Boeing won a contract for the supply 50 Apache helicopters to the British Army, which could now be scrapped, according to commentators.