The defence giant's stock fell 4.6 per cent on the New York Stock Exchange in early trade, down to $247.61, after the President-elect tweeted that the F-35 programme and its cost is "out of control".
Based on Lockheed Martin's number of shares outstanding, the single Twitter swipe has trimmed $4bn off the group's market value.
"Billions of dollars can and will be saved on military (and other) purchases after January 20th [when the Trump will enter the White House]," Trump said.
The F-35 program and cost is out of control. Billions of dollars can and will be saved on military (and other) purchases after January 20th.— Donald J. Trump (@realDonaldTrump) December 12, 2016
The F-35 jet is a single-seat, single-engine fighter jet that is being principally funded by the US. The UK has been named as a global repair hub for the jets.
In response to Trump's tweet, Jeff Babione, Lockheed Martin's F-35 programme leader, said: "Since the beginning, we have invested hundreds of millions of dollars to reduce the price of the airplane by about 70 per cent since its original costing, and we project it to be about $85m in the 2019 or 2020 time frame."
A week before Trump won the 8 November presidential election, the US Defense Department and Lockheed Martin concluded negotiations on their ninth contract for F-35 fighter jets after 14 months of negotiations on the deal of more than $6.1bn (£4.8bn), the Pentagon said.
Trump frequently took the social media site during his election campaign and doesn't seem to be slowing down (or handing it over to a PA) now that he is preparing for his time as leader of the free world.
Through his account he has taken aim at everyone from Republican senator John McCain, Hillary Clinton, the editorial board of the Wall Street Journal and European leaders.