JetBlue Airways Corp. is urging U.S. regulators to reject Boeing Co.’s fair-trade complaints against Bombardier Inc. as the New York-based airline considers adding new planes to its fleet. Boeing’s claim that Bombardier sold its C Series jets in the U.S. at less than fair value thanks to Canadian government subsidies presents “a threat to JetBlue’s ability to continue to innovate and provide benefits to the flying public,” Chief Executive Officer Robin Hayes said in a letter filed Monday with the U.S. International Trade Commission. JetBlue plans to decide by the end of the year on changes to its fleet, including whether to replace its Embraer SA E190s, possibly with the C Series. The airline has held talks off-and-on with Bombardier, Bloomberg reported last year. In his letter, Hayes urged the commission “to reject the petitions and permit free and unfettered competition in the aircraft manufacturing sector.” The letter was first reported by FlightGlobal, a trade publication. The C Series is the only aircraft offering five seats abreast, aligning it with JetBlue’s “history of product differentiation,” he said, and has potential to reduce operating costs in line with JetBlue’s low-cost model. Boeing makes no comparable aircraft, the letter said. Airline Supporters JetBlue currently flies planes made by France’s Airbus SE and Brazil’s Embraer. It’s at least the third airline to file a letter in support of Bombardier that doesn’t operate its planes, following Spirit Airlines Inc. and Sun Country Airlines Inc. The letter reflects JetBlue’s general position that competition is good for the airline industry, said Doug McGraw, a spokesman. Boeing had no immediate comment, said Dan Curran, a spokesman. The U.S. Commerce Department will release a preliminary ruling Tuesday on whether to impose countervailing duties on Bombardier. Boeing says Bombardier was able to offer attractive pricing to Delta Air Lines Inc. last year—in a deal for at least 75 aircraft—because of government assistance. Quebec’s provincial government invested $1 billion last year for a 49.5 percent stake in the C Series, and its federal counterpart followed this year with a C$372.5 million ($301 million) financing package for two of Bombardier’s jet programs, including the C Series. In June, the U.S. trade commission ruled that Boeing’s commercial jet business may have been harmed by Bombardier.