The World Trade Organization has reportedly ruled that the European Union gave illegal subsidies to Airbus.
The Wall Street Journal reported the decision, which is confidential.
US and European diplomats have declined to release the ruling, which is over 1000 pages long.
The ruling comes after five years of deliberations. The decision is not expected to be officially made public for at least several months.
The trade dispute between the aircraft manufacturers, Boeing in the United States and Airbus in Europe, is the biggest in the WTO's history.
The EU has also made a counter claim against the US for its support of Boeing. The BBC reports a ruling on this claim is due in the next six to eight months.
