"The C Series would not even exist at this point but for those subsidies", Boeing said, adding that the support enabled the company "to dump aircraft into the US market at absurdly low prices".
Commerce Secretary Wilbur Ross said the decision was based on a "full and unbiased review of the facts in an open and transparent process".
The Commerce Department's tariff will only take effect if the US International Trade Commission (ITC) rules in Boeing's favour in its final decision, which is expected in early 2018.
The department has imposed tariffs of almost 300 per cent on imports of the jet after rival Boeing complained that it had received unfair subsidies.
"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 said in a news release.
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.
Bombardier has yet to ship any of the planes to the United States. The complaint found a receptive ear in President Donald Trump, whose "America First" agenda has included taking a tough line in matters of worldwide commerce.
Boeing called for action from U.S. authorities saying the C-Series competes with its small 737 jet, a point refuted by Bombardier.
He also added: "We would urge the US International Trade Commission to do the right thing for fair trade and jobs by finding against Boeing and setting aside the commerce department's determination when it makes its final decision in the New Year".
The Administration's approach aligns with Boeing's long-term effort to push back against improper government subsidies to competitors, even as the company has been found by the World Trade Organisation to benefit from more than $1 billion of unfair benefits from the state of Washington.
"Unfortunately, the Commerce Department decision is divorced from this reality and ignores long-standing business practices in the aerospace industry, including launch pricing and the financing of multibillion dollar aircraft programs", Bombardier said.
Bombardier doesn't deny that Delta received a good price.
"There's no case here", Bombardier's Bellemare said, calling the complaint "ridiculous".
The question now before the ITC is whether those improper benefits injured Boeing in the 100-150-seat market for commercial aircraft.
Delta plans to use the fuel-efficient but small mainline aircraft to operate flights to a broader array of midsize markets than it can efficiently do with its present fleet.