Shares in Lockheed Martin have fallen after President-elect Donald Trump said he would cut the cost of its F-35 Joint Strike Fighter after taking office.
He tweeted: "F-35 program and cost is out of control. Billions of dollars can and will be saved on military (and other) purchases after January 20."
The F-35 is the Pentagon's most expensive weapons programme, costing about $400bn (£316bn).
Lockheed shares were down 4.2% at $248.51 in morning trading.
Jeff Babione, Lockheed's F-35 chief, said the company understood concerns about affordability, but added: "It's an amazing programme. It's great value and I look forward to any questions that the President-elect may have."
He was in Israel on Monday with US Defence Secretary Ash Carter as the country prepared to take delivery of first F-35 fighters.
Israel is among a small number of US allies to buy the plane.
Mr Trump's missive comes a week after he condemned as "out of control" the cost of a new Air Force One plane being built by Boeing.
Israel - which signed a deal this year for $38bn in US military aid - has ordered 50 of the new fighter jets, each priced at around $100m.
Trump and Twitter
Donald Trump's Twitter account wasn't always the powerful spectacle it has become.
His interaction with Twitter began much like any other high profile account managed by a group of marketing professionals.