Delta Air Lines was originally expected to receive the first of its firm order for 75 CS100 planes next spring, but now plans to wait until the aircraft destined for US customers will be built from the Airbus manufacturing plant in Alabama.
In response to the complaints, the U.S. Department of Commerce levied duties of close to 300% on Bombardier's aircrafts.
Boeing launched the trade case in April, arguing that governments in Canada and Britain subsidized the plane's development which allowed Bombardier to sell it at unfairly low prices.
"The Commerce Department announced total duties of 292.21 percent - a final antidumping rate of 72.82 percent and a final countervailing duty rate of 212.39 percent - in a case brought by Chicago-based Boeing".
"The United States is committed to a free, fair and reciprocal trade and will always stand up for American workers and companies being harmed by unfair imports", he adds.
Under a newly forged Bombardier-Airbus partnership a new manufacturing plant will be built in Alabama where the planes will be assembled, providing a possible avenue to avoid the hefty duty.
In a twist, European aerospace company Airbus, Boeing's chief rival, swooped in October, agreeing to buy a majority stake in the struggling C Series program.
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The Commerce Department's decision comes as the Trump Administration takes a hard line on trade practices it views as hurting American workers.
"Today's decision validates Boeing's complaints regarding Bombardier's pricing in the United States, pricing that has harmed our workforce and US industry", it added.
The International Trade Commission will make its final injury determination by February 1, and if injury is found, Commerce will issue AD and CVD orders.
The inquiry now moves to the United States global trade commission, which will examine if the dumping and subsidies caused injury to Boeing.
"Tariffs on the scale proposed by the US Commerce Department in the world's largest airline market, threaten to undermine the long-term economics of Bombardier's presence in Northern Ireland".
Bombardier doesn't deny that Delta received a good price. Bombardier calls Boeing's criticism unfounded, saying that the USA company's entire case has been overtaken by events. Boeing, Bombardier and Delta presented arguments to the ITC this week. But the panel also appeared dubious about Bombardier's claims that the CSeries and the smallest versions of the 737 do not compete against each other at all.
The move affects 100- to 150-seat large civil aircraft from Canada.