British Labour Party leader Jeremy Corbyn has stepped up the pressure on Prime Minister Theresa May to intervene in the trade dispute with the US threatening hundreds of jobs in the Belfast factory of planemaker Bombardier.
In a letter to Mrs May, the Labour leader (pictured) urged her to join with Canadian premier Justin Trudeau in summoning the head of Boeing to an "urgent summit" to demand the US aerospace giant drops its claim against Bombardier.
In a preliminary ruling the US Department of Commerce, imposed a 220% tariff on Bombardier's new C-Series jets following a complaint by Boeing that it's Canadian rival had received subsidies from the Canadian and British governments.
The decision is threatening to derail a major contract with Delta Airlines - jeopardising jobs at Bombardier's Belfast plant, which employs more than 4,000 people and which builds the wings for the C-Series aircraft.
In his letter, Mr Corbyn accused Mrs May of "foot-dragging" over the issue, saying that while she had raised the matter directly with President Donald Trump, she had so far failed to secure a resolution to the dispute.
He urged her to act with "strength of purpose" and join Mr Trudeau in confronting Boeing chairman and chief executive Dennis Muilenburg to make clear the firm must now withdraw its claim.
He said that the dispute showed the dangers of relying on a free trade deal with the US once Britain has left the EU.
"Your own discussions with President Trump, now over three weeks ago, have not resulted in the resolution of this dispute," he said.
"You must now realise that the aggressive and protectionist way the US government conducts its trade relations with other countries is not conducive to the swift and beneficial post-Brexit trade agreement that you and your ministers have so often suggested.
"You must now act with strength of purpose in the national interest."