Boeing has hit out at rivals Airbus and Bombardier after the two announced what it called a "questionable deal" late last night.
Airbus agreed to take a majority stake in Bombardier's C Series jetliner programme, giving the Canada-based Bombardier a boost as it deals with an ongoing trade dispute with US firm Boeing.
Europe's Airbus will hold a 50.01 per cent stake in the C Series Aircraft Limited Partnership, which makes and sells the jets, under the deal, and Bombardier said the partnership was expected to more than double the value of the programme.
Earlier this month, the US Department of Commerce said it would impose a further 80 per cent tariff on the import of Bombardier's C Series jet to the US after Boeing complained Bombardier was dumping aircraft in the US market.
Now, Airbus has offered to assemble some C Series jets at its plant in Alabama for US orders, meaning they would not be subject to the possible 300 per cent US tariff.
A Boeing spokesperson said: "This looks like a questionable deal between two heavily state-subsidised competitors to skirt the recent findings of the US government. Our position remains that everyone should play by the same rules for free and fair trade to work."
UK business secretary Greg Clark said the move was a "step forward" after the high tariffs had threatened to put Bombardier's huge Northern Ireland plant at risk.
Clark said: “Since Boeing initiated action against Bombardier, we have been active alongside our Canadian counterparts to work to secure the future of the C Series and safeguard jobs and manufacturing at Bombardier Shorts in Belfast, and the supply chain across the UK.
"We will continue to work closely with the companies to protect UK interests and with the Canadian government to ensure the unjustified case brought by Boeing is brought to a swift resolution."
The GMB union's national officer Ross Murdoch said it was "potentially good news for our members in Belfast".
"But, as always, the devil will be in the detail."
Airbus and Boeing are embroiled in their own row over aerospace subsidies through the World Trade Organisation, which is expected to come to a head soon.