Still pending is a final determination by the Commerce Department in December and by the U.S. International Trade Commission in February.
Delta announced the deal with Bombardier in April 2016 to buy 75 CS100 jets to be configured with about 110 seats each.
Delta would start flying the planes in spring 2018.
The order could be valued at $5.6 billion, but airlines typically negotiate steep discounts for large plane orders. Scoring the Delta order was also a big win for Bombardier, in competition against heavyweights Boeing and Airbus.
When announcing the order, Delta CEO Ed Bastian called the deal "opportunistic". He said he believed Delta's order made Bombardier "a third competitor," along with Boeing and Airbus, "and we're thrilled to be able to have that choice in the marketplace."
Delta in a written statement Tuesday emphasized that the Commerce Department’s decision is preliminary and that the International Trade Commission’s determination will be the “real decision.”
“We are confident the USITC will conclude that no U.S. manufacturer is at risk because neither Boeing nor any other U.S. manufacturer makes any 100-110 seat aircraft that competes with the CS100,” Delta said.
“Boeing had the chance to compete with Bombardier for Delta's purchase of aircraft in this size range, but Boeing's only proposed alternative to the CS100 was to offer Delta used Brazilian-made regional jets,” Delta said. “Boeing has no American-made product to offer because it cancelled production of its only aircraft in this size range - the 717 - more than 10 years ago.”
Delta struck a deal in 2012 for used Boeing 717s from Southwest Airlines, which inherited the jets from AirTran Airways in a merger.
Bombardier issued a statement saying: “The magnitude of the proposed duty is absurd and divorced from the reality about the financing of multibillion-dollar aircraft programs.”