Thousands of jobs at one of Northern Ireland's largest employers, aeroplane manufacturer Bombardier, may be under threat after the US Department of Commerce (DoC) announced plans for a punitive 220% tariff on imports of one of its models.
Here are some key questions:
What is the row about?
It centres on US-based Boeing's allegations that Canadian-headquartered Bombardier received state subsidies allowing it to sell its C-Series planes at below-market prices in America.
The DoC has carried out its own investigation and said it had made a preliminary determination that imports should be subject to a 219.63% import tariff, although it will continue to evaluate the figure.
If the tariff is imposed when deliveries of the aircraft begin it will increase the cost of selling into one of the world's most important aviation markets.
Bombardier is contracted to supply up to 125 C-Series aircraft to Atlanta-based Delta Airlines in a deal underpinning many staff posts at its manufacturing plant in Belfast.
The UK Government has been actively lobbying in the US for a compromise between Boeing and Bombardier amid growing concern about the potential implications for Bombardier's Northern Ireland operations.
What are the aerospace companies saying about it?
Boeing submitted a petition with the US International Trade Commission and the Department of Commerce in April which claimed large government subsidies helped Bombardier launch an aggressive campaign to "dump" its C-Series aircraft in the US.
It said there was a shared industry interest in a level playing field.
Bombardier has repeatedly rejected Boeing's claims, accusing its rival of pure hypocrisy after it alleged anti-competition practices in the sale of aircraft.
The manufacturer described the DoC's interim determination as "absurd" and "divorced from the reality about the financing of multi-billion-dollar aircraft programmes".
What are the implications for Belfast?
Bombardier had been under financial pressure and invested large sums in its new jet programme, which is crucial to many jobs in the city.
Last year the firm announced 1,080 job losses at its Northern Ireland plants following delays to the C-Series.
It is one of the country's largest employers, with around 4,500 on the books. According to the GMB union it supports nearly 10,000 further jobs through its suppliers.
What is the Government doing about it?
Political powersharing at Stormont has been in cold storage for months. However the DUP's 10 anti-Brexit MPs are a crucial force propping up the Government in key votes after Theresa May lost her majority in this year's General Election.
DUP leader Arlene Foster's influence has seen the Prime Minister lobbying US President Donald Trump during a recent visit to New York.
Following the DoC's announcement the UK Government said it would "continue to strongly defend UK interests" and labelled Boeing's position as "unjustified".