Boeing has accused its Canadian rival of benefiting from government subsidies, allowing it to sell its new C-Series planes to U.S. buyers at below cost.
The particular case arose from Bombardier's 2016 deal to sell 75 C-Series jets to Delta Air Lines. Boeing claims Delta bought the planes at $20 million each, enjoying a hefty discount from the list price of $33 million. Those figures have not been confirmed by either Bombardier or Delta.
At the hearing Monday, Boeing said that Bombardier's use of Canadian public cash had allowed it to discount its planes to the point that Boeing's new 737s were not as competitive in the U.S.
Bombardier countered that Boeing's hefty order book suggested otherwise and that Boeing was making money "hand over fist."
Some analysts have suggested Boeing was emboldened to take legal action after Washington laid out its "America First" ethos for trade.
The U.S. Commerce Department has already ruled in Boeing's favor. In October, it slapped a 300 percent tariff on the Bombardier C-Series jets.
Head of Aviation at IHS Markit, John Sneller, said Tuesday that the ITC findings should be revealed Tuesday and there is some chance that the tariff ruling could be overturned.
"Discounting of airlines is not unusual. This is probably a little more aggressive than you would normally see. So up to 50 percent for a large order is not unusual. This is closer to 60 or 70 percent," he said.
"Also the evidence isn't very strong that Boeing's order book has been affected adversely," Sneller told CNBC.