The dispute centers on alleged illegal subsidies that Bombardier received for its C-Series program, a 100 to 150-seat jet that has been in the skies since 2016.
The U.S. Commerce Department, with the support of President Donald Trump, took up a Boeing complaint that Bombardier received state aid as far back as 2008 in order to make the program a success. Boeing's second part of the complaint was that Bombardier could potentially "dump" the aircraft to buyers at below-market prices.
Boeing has also claimed that Bombardier's deal with Delta Airlines will see 75 C-Series planes sold for $19.6 million apiece, way below production cost.
The Department of Commerce asked Bombardier to provide information but the Canadian company refused, claiming it would provide rivals with a look into its business and pricing structure.
After this refusal, U.S. authorities upheld the Boeing complaint and issued Bombardier with a preliminary 300 percent anti-dumping tariff on its C-Series.
The CS100 and CS300 versions of the Bombardier plane are in use by Swiss Air and Air Baltic. In the United States, Bombardier has sold 75 of its new C-Series planes to Delta Airlines.