The U.S. threatened to impose sanctions against the European Union after the World Trade Organization ruled that Airbus SE received illegal government funding to develop jetliners, costing Boeing Co. sales.

The final decision affirmed a 2016 finding that the EU had failed to eliminate unfair subsidies for two Airbus twin-aisle models, ending a long-running trade case. The international court is expected to rule later this year on a separate case in which the EU challenged billions of dollars in U.S. tax incentives to Boeing.

The litigation adds to the tension between the U.S. and Europe, two once-cooperative trade partners that are already sparring over U.S. President Donald Trump's steel and aluminum tariffs and his decision to back out of a nuclear treaty with Iran, jeopardizing $40 billion in aircraft sales.