The United States Department of Commerce has issued a preliminary ruling to impose a 219.63% tariff on all Bombardier Aerospace C Series imports. Should the determination be upheld by the US International Trade Commission (USITC) in early 2018, the new tariff will apply to the import of all Canadian large civil aircraft of 100- to 150-seats.

“The U.S. values its relationships with Canada, but even our closest allies must play by the rules,” said US Secretary of Commerce Wilbur Ross. “The subsidization of goods by foreign governments is something that the Trump Administration takes very seriously, and we will continue to evaluate and verify the accuracy of this preliminary determination.”

The decision came after Boeing lodged a formal complaint accusing the Canadian manufacturer of dumping. In its petition, Boeing contends that Bombardier sold seventy-five CS100 jets to US carrier Delta Air Lines (DL, Atlanta Hartsfield Jackson) for USD19.6 million per aircraft, far below their USD33.2 million manufacturing cost, and that the C Series could never have existed without subsidies from the governments of Canada, Quebec and the United Kingdom.

"The US Department of Commerce today affirmed that Bombardier has taken massive illegal subsidies in violation of existing trade law," Boeing said in a statement.

Responding to the Commerce department's preliminary ruling, Bombardier says the magnitude of the tariff is "absurd and divorced from the reality about the financing of multibillion-dollar aircraft programs". It accuses Boeing of using a skewed process to "unfairly tilt the playing field in its favour".

The Trump administration's decision has also raised the ire of the British government, with Defence Minister, Sir Michael Fallon, saying that Boeing's behaviour "could indeed jeopardise our future relationship with them". About 1,000 British workers are involved in the manufacture of the C Series. Quebec premier Philippe Couillard was even more strident, saying that Quebec had been 'attacked' and that the state would 'resist'. "All together we will protect our workers. All together we will be proud of our engineering," Couillard said.

Canada's Prime Minister Justin Trudeau has yet to formally comment on the announcement, but has previously been clear that it could affect Canada's relationship with Boeing. "Certainly we won't deal with a company that's attacking us and attacking thousands of Canadian jobs," Trudeau said.

Opponents of the United States' decision hope that the USITC will recognise that the C Series does not compete with any Boeing product, and so the American manufacturer cannot have suffered any material loss.