Quebec Premier Philippe Couillard says he wants Ottawa to take a hard line against Boeing after the U.S. Department of Commerce proposed a hefty 219 per cent countervailing duty on jets manufactured by Montreal rival Bombardier.

The department's preliminary findings released Tuesday concluded Bombardier benefited from improper government subsidies, giving it an unfair advantage when selling its CSeries jets south of the border.

Couillard disagreed, saying the US$1 billion invested by the province in the CSeries program was not a subsidy and that no other investment in Bombardier was currently planned.

The company is being targeted by its larger U.S.-based aerospace rival even though Boeing has also benefited from decades of government assistance, the premier told a news conference Wednesday.

Boeing may have won this battle, but haven't won the war, he added as he urged the Trudeau government to continue taking a hard line with Boeing until the dispute can be settled for good.

"Not a bolt, not a part, (and) of course not a plane from Boeing (should be) entering Canada until this conflict is resolved in a satisfactory way," Couillard said in Quebec City.

"How could we justify doing business with a company that wants to destroy Canadian jobs in aerospace?" Couillard continued. "I'm very happy Mr. Trudeau has reacted until now and I know he will continue doing the same."

Couillard said Tuesday's announcement was not a positive development in U.S.-Canada relations. Nonetheless, the Quebec government will continue to promote open markets, he said.

The U.S. workforce is also impacted by CSeries to the tune of 22,000 related jobs and an economic impact of $30 billion, he added. "To damage this will be to damage the U.S. economy."

British Prime Minister Theresa May also weighed in Wednesday on the decision, tweeting that she was "bitterly disappointed" in the finding.

She said her government "will continue to work with the company to protect vital jobs for Northern Ireland," where Bombardier employs more than 4,000 people at its factories in Belfast.

Noted Couillard: "Boeing may have created something they won't (be able to) control anymore, and they may come to regret that decision."