DUP leader Arlene Foster has said that her party would seek to use its influence over the British government in the Bombardier dispute.
It comes after the US Department of Commerce decided to impose a 219% levy on the delivery of each airliner.
There are fears that the US trade ruling could put around 1,000 jobs at risk.
Mrs Foster described the trade ruling as "completely unjustifiable".
She told Sky News: "Everyone realises how important Bombardier is to Northern Ireland and we will use our influence with our government to make sure that continues.
"What we must do now is to continue to work with our own government, with the American government, with the Canadian government, in trying to get Boeing to see sense.
"This is a completely unjustifiable complaint and therefore we have to work with them to make them see that, and to work with the company as well."
The preliminary ruling upholds a claim by the Canadian company's American rival Boeing that Bombardier has been unfairly subsidised by the British and Canadian governments.
British Defence Secretary Michael Fallon meanwhile, warned that Boeing's behaviour could jeopardise its trading relationship with the Britain.
He said its stance could risk lucrative defence contracts with the UK.
Mr Fallon said: "Boeing is a major defence partner and one of the big winners of the latest defence review so this is not the kind of behaviour we expect from a long-term partner.
"This is not the behaviour we expect of Boeing and could indeed jeopardise our future relationship with Boeing."
He added: "Boeing stand to gain a lot of British defence spending. We have contracts in place with Boeing for new maritime patrol aircraft and for Apache attack helicopters and they will also be bidding for other defence work and this kind of behaviour clearly could jeopardise our future relationship with Boeing."
A spokesperson for British Prime Minister Theresa May said she was "bitterly disappointed" by the ruling, adding: "The government will continue to work with the company to protect vital jobs for Northern Ireland."
Mrs May had lobbied US President Donald Trump over the dispute.
A spokesperson for Bombardier has said that ultimately she believes the International Trade Commission will see that Bombardier is in the right.
Speaking on RTÉ's News at One, , Haley Dunne,Dunne said that Bombardier employees could be reassured that tireless work was being done to reverse the decision.
"We have industry experts, analysts, airlines that aren't even our customers at this point, coming out, writing to their congressmen, speaking out about the importance of this aircraft to competitiveness in the market, but also about the meritlessness of this petition from Boeing.
"So we do have a huge force behind us, including our governments. We are working tirelessly to resolve this."
A leading member of the DUP has said that although the decision on Bombardier is an interim one, it "smacks of protectionism".
Also speaking on the News at One, Jeffrey Donaldson said if "that's the route America decides to choose, they need to remember that it's a big world, that they export a lot of their goods around the world and that American companies do a lot of business in the UK."
Mr Donaldson added that Boeing should "wind your neck in, remember that you need to do business around the world, that there's a big market, a global market that Boeing needs to sell aircraft into".
US Secretary of Commerce Wilbur Ross said: "The US values its relationships with Canada, but even our closest allies must play by the rules.
"The subsidisation 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."
Bombardier, which is due to begin delivering a blockbuster order for up to 125 new C-Series jets to Atlanta-based Delta Airlines next year, now faces paying a punitive tariff on its exports of planes to the US.
The US Department of Commerce has imposed an intermediary countervailing duty of 220%. This is an import tax imposed on certain goods in order to prevent dumping or counter export subsidies.
The UNITE union has said it is acutely disappointed and that the ruling poses a direct and very serious threat to the 4,500 jobs in Bombardier Belfast and many more dependent on the company.
The Commerce Department's penalty against Bombardier will only take effect if the US International Trade Commission rules in Boeing's favour in a final decision expected early next year.
Boeing said in a statement: "This dispute has nothing to do with limiting innovation or competition, which we welcome. Rather, it has everything to do with maintaining a level playing field and ensuring that aerospace companies abide by trade agreements."
To win its case before the ITC, Boeing still faces the challenge of proving it was harmed by Bombardier's sales practices, despite not using one of its own jets to compete for the Delta order, Dan Pearson, a senior fellow at the libertarian Cato Institute think tank in Washington, said before today's announcement.
"This (ITC case) cannot be a slam dunk," said Pearson, a former ITC chairman. "I'm having a hard time figuring out how Boeing was harmed by this."
