(Adds detail on duties)
WASHINGTON, Oct 6 (Reuters) - The U.S. Commerce Department on Friday moved to impose additional trade duties on the sale of Bombardier Inc CSeries jets in the United States, prompted by Boeing Co's complaint that the Canadian company had dumped the planes at "absurdly low" prices.
The Commerce Department proposed a 79.82 percent antidumping duty after a preliminary finding that the jets were sold below cost to Delta Air Lines in 2016.
The decision is expected to heighten trade tensions that flared last week after the United States announced a preliminary duty of nearly 220 percent for subsidies Bombardier received, which was well above the 80 percent duty Boeing sought in its complaint.
Canada and Britain threatened to avoid buying Boeing military equipment in retaliation, saying the duties on the CSeries would reduce U.S. sales and put thousands of Bombardier jobs in their countries at risk.
The combined duty of 299.45 percent would be applied to the cost of the plane imported to the United States, effectively keeping it out of the market, but would only take effect if the U.S. International Trade Commission rules in Boeing's favor in a final decision expected in early 2018.
Bombardier shares dipped 2 cents to C$2.18 immediately after the announcement but have since recovered.
(Reporting by Alwyn Scott, Tim Ahmann and Allison Lampert; Editing by Meredith Mazzilli)