The United States department of commerce has again ruled in favour of US-based airline manufacturer Boeing in a dispute with rival Bombardier.
The decision will see a further 80 per cent tariff added to imports of the Bombardier C-Series planes when imported to the United States.
This is on top of a 220 per cent tariff imposed last month.
Boeing accuses its rival of receiving state subsidies from the Canadian and British governments, allowing it to sell aircraft in the US for below cost price.
There have been warnings in the UK that the import tariffs could threaten Bombardier jobs in Belfast.
About 1,000 jobs are linked to the C-Series, the wings of which are made at a purpose-built £520m factory in the city.
A spokesperson for Bombardier said: “We strongly disagree with the commerce department’s preliminary decision.
“This hypocrisy is appalling, and it should be deeply troubling to any importer of large, complex, and highly engineered products.”
The US department of commerce rulings, which could more than triple the cost of a C-Series aircraft sold into the US, could jeopardise a major order placed last year from US airline Delta.
“The United States is committed to free, fair and reciprocal trade with Canada, but this is not our idea of a properly functioning trading relationship,” said US commerce secretary Wilbur Ross.
“We will continue to verify the accuracy of this decision, while do everything in our power to stand up for American companies and their workers.”
A final decision is expected next year.