The U.S. Department of Commerce on Tuesday proposed a 219.63 percent duty on the sale of 100- to 150-seat jets from Canada into the U.S., potentially striking a major blow to Bombardier’s C Series program. The ruling comes ahead of planned delivery next spring of the first of 75 Bombardier CS100s to Delta Air Lines, the U.S. launch customer for the program.

The determination stems from a complaint filed by Boeing with the International Trade Commission in April that Bombardier sold the narrowbody jets for well below their cost of manufacture with the help of improper subsidies from the province of Quebec and the Canadian federal government. Bombardier has vigorously contested both the basis of the claims and the cost estimates provided by Boeing in its complaint. The U.S. company claims Bombardier sold the airplanes for $19.6 million each, or some $13.8 million less than they cost to manufacture. The Commerce Department said it arrived at its subsidy estimate based on information from the Canadian manufacturer itself and the governments of Quebec, Canada and the UK, where Bombardier builds most of the airplane’s composite wings at its Short Brothers plant in Belfast, Northern Ireland.

“The magnitude of the proposed duty is absurd and divorced from the reality about the financing of multibillion-dollar aircraft programs,” said Bombardier in a statement following the Commerce Department’s announcement. “This result underscores what we have been saying for months: the U.S. trade laws were never intended to be used in this manner, and Boeing is seeking to use a skewed process to stifle competition and prevent U.S. airlines and their passengers from benefiting from the C Series.”

Delta’s order came six months after the province of Quebec agreed to infuse $1 billion in the then-financially strapped C Series program, giving it a 49.5-percent stake in a limited partnership with Bombardier. Less than a year later the Canadian federal government agreed to grant Bombardier C$372.5 million in interest-free loans for both the C Series and the Global 7000 business jet.

The Commerce Department said it would instruct U.S. Customs and Border Protection to collect cash deposits from importers of 100- to 150-seat civil aircraft based on its preliminary determination. “The U.S. values its relationships with Canada, but even our closest allies must play by the rules,” said Secretary 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.”

Next, the International Trade Commission must determine that the subsidies to Bombardier harmed Boeing before it begins to impose any tariffs. Schedules call for the Department of Commerce to announce final determination on December 18 and the International Trade Commission to issue its final determination on February 1. If both rule in the affirmative, tariffs would take effect on February 8. Bombardier argues that the C Series competes with no Boeing product, and therefore could not have caused any harm to the U.S. company.

“We produce a product that competes in a size category where Boeing does not compete,” Bombardier Commercial Aircraft CEO Fred Cromer said during a briefing with reporters at the company’s facilities in Mirabel, Canada, on September 12. “We have airlines—specifically Delta—that have been very vocal about the fact that Boeing was not included in their process because they don’t have an aircraft in the size category that they’re looking for. So if you take a step back and you look at the facts of the case, I think the facts favor our position.”

Bombardier has announced plans to boost C Series production from seven airplanes in 2016 to between 90 and 120 airplanes by 2020. It expects to ship 30 of the jets this year.