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Boeing late Monday dismissed a deal between Airbus and Bombardier to make CSeries jets in Alabama, calling it an attempt to dodge import duties recommended by the U.S. Commerce Department following the U.S. airplane maker’s trade complaint.

"This looks like a questionable deal between two heavily state-subsidised competitors to skirt the recent findings of the U.S. government," a Boeing spokesman said.

"Our position remains that everyone should play by the same rules, for free and fair trade to work."

Earlier Monday, Airbus announced it would buy a majority stake in Bombardier’s CSeries program, giving the Canadian company an unexpected boost in its costly trade dispute with Boeing.

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A Bombardier CS300 aicraft takes off as an Airbus A380 waits on the taxiway in this file photo. Pascal Rossignol / Reuters

Under the deal, some of the CSeries will be produced in the United States where local airlines — notably Delta, which has ordered 75 aircraft — would not have to pay a threatened 300 percent duty on U.S. imports.

Airbus Chief Executive Tom Enders said the company has offered to assemble some of the jets at its plant in Alabama.

The U.S. assembly line would mean the jets would not be subject to possible U.S. anti-subsidy and anti-dumping duties, Bombardier Chief Executive Alain Bellemare said on a media conference call.

Bellemare called the deal with Airbus, which was first attempted unsuccessfully in 2015, a "strategic" decision that is expected to close in the second half of 2018.

"We're doing this deal here not because of this Boeing petition. We are doing this deal because it is the right strategic move for Bombardier. And it makes good strategic sense for Airbus," Bellemare said.

The Boeing-Bombardier dispute has snowballed into a bigger multilateral trade dispute, with British Prime Minister Theresa May wading into the debate and asking U.S. President Donald Trump to intervene in order save British jobs.

Bombardier is the largest manufacturing employer in Northern Ireland, which is the poorest of the United Kingdom's four nations and remains mired in political sensitivities after emerging from decades of armed sectarian conflict.

Delta said it looked forward to introducing the CSeries into its fleet.

Bombardier is in the middle of a five-year turnaround plan after considering bankruptcy because of a cash-crunch after developing multiple plane programs simultaneously including the CSeries.