China is going after Boeing, America’s biggest exporter, in its trade war with the U.S. Beijing has told Chinese airlines not to place new orders for Boeing jets and is requiring carriers to seek approval before taking delivery of aircraft they have already ordered,

Boeing has delivered 18 aircraft to nine Chinese airlines so far this year, numbers show. However, they have been told not to accept any further deliveries.

Boeing shares were lower early Tuesday after a report that China ordered its airlines not to take any more deliveries of U.S.-made jets.