Theresa May phoned President Trump to ask him intervene in a bitter aerospace trade dispute that threatens thousands of jobs in Belfast.
Canadian aerospace giant Bombardier, which employs around 4,500 people in Belfast and accounts for 10% of the north's manufacturing exports, is facing significant costs in a spat with US aeronautics powerhouse Boeing.
The dispute centres over Boeing's allegations that Bombardier received subsidies allowing it to sell its CSeries planes at below-market prices. The US Department of Commerce is expected to announce a decision on whether to impose duties against Bombardier on September 25.
In a statement released this morning, Boeing said it is seeking "to restore a level playing field in the US single-aisle airplane market."
The statement said: "Boeing had to take action as subsidised competition has hurt us now and will continue to hurt us for years to come," the company said in a statement.
"This is the normal course of action for addressing instances where a competitor is selling into the US market below cost, and we will let the process play out.
"We believe that global trade only works if everyone plays by the same rules of the road, and that's a principle that ultimately creates the greatest value for Canada, the United Kingdom, the United States, and our aerospace industry," the company added.
The British government has been actively lobbying in the US for a compromise between the two companies amid growing concern about the potential implications for Bombardier's Belfast operations.
Prime Minister Theresa May raised the matter with the US president in a phone call last week.
Business Secretary Greg Clark also recently travelled to Boeing's base in Chicago to discuss the potential impact of the dispute and Northern Ireland Secretary of State James Brokenshire has been involved in negotiations.
The fact Downing Street has become involved demonstrates the level of concern over the impact an adverse ruling by the US Department of Commerce against Bombardier could have on the future of the Northern Ireland factory.
Around 1,000 of Bombardier's Belfast employees are involved in the making of the CSeries wings at the centre of the US-Canadian trade dispute.
Boeing filed a petition with the US International Trade Commission and the US Department of Commerce in April, alleging that massive subsidies from the Canadian government have allowed Bombardier to embark "on an aggressive campaign to dump its CSeries aircraft in the United States".
Bombardier has rejected Boeing's claims. Bombardier said the plaintiff is a global powerhouse that has not lost any sales as a result of Bombardier.
A British government spokesman said: "This is a commercial matter but the UK Government is working tirelessly to safeguard Bombardier's operations and its highly skilled workers in Belfast.
"Ministers across government have engaged swiftly and extensively with Boeing, Bombardier, the US and Canadian governments. Our priority is to encourage Boeing to drop its case and seek a negotiated settlement with Bombardier."
