Boeing faces a $9bn hit for illegal subsidies in the latest battle in a long-running transatlantic trade war.
The World Trade Organisation is expected to say this week that tax breaks given to the US plane-maker broke international rules, and it will have to pay them back.
America and Europe have been engaged in a 12-year battle over state support for their aircraft industries, with the US championing Boeing and the EU fighting for Airbus.
However, there are concerns that the dogfight over subsidies between Boeing and Airbus – who between them dominate the commercial aircraft market – could mean they risk losing their supremacy to new players.
The latest claim relates to an incentive Boeing was given by Washington State, which almost halved its tax rate to encourage the plane-maker to develop its new 777-X airliner there.
Industry sources say Boeing benefited by between $2bn and $9bn from the tax break, which the WTO could order it to repay as soon as Monday.
The move comes two months after Boeing claimed a major victory in the row when the WTO ruled that the EU had not stopped billions in state aid to Airbus. The international trade referee said that without this funding, Airbus’s latest A350 jet would never have got off the ground.