President-elect Donald Trump took a swipe at Lockheed Martin's F-35 program Monday morning, saying the cost was "out of control."

Shares of the aerospace company dropped more than 4 percent in early trade. The company's market value dropped $4 billion after the tweet. The impact of Trump's tweet, per character, was more than $28 million.

Trump tweeted that "billions of dollars can and will be saved on military (and other) purchases" once he takes office in January.

Donald J. Trump @realDonaldTrump

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.

8:26 AM - 12 Dec 2016

Lockheed Martin has invested large sums of money to reduce the price of the F-35 stealth fighter program, a company executive said in Israel on Monday, responding to Trump's criticism.

"Since the beginning, we have invested hundreds of millions of dollars to reduce the price of the airplane by about 70 percent since its original costing, and we project it to be about $85 million in the 2019 or 2020 time frame", Jeff Babione, Lockheed Martin's F-35 program leader told Reuters.

The company added it will welcome "the opportunity to address any questions the president-elect has about the program."

When Trump's transition team was asked by reporters about Trump's tweet, the team said a clear message is being sent that Trump will fight for taxpayers.

After the tweet, shares of defense stocks Boeing and General Dynamicsalso were trading down, 0.72 percent and 2.87 percent, respectively. Defense ETF's PowerShares Aerospace & Defense Portfolio and iShares U.S. Aerospace & Defense were down more than 1 percent.

A week before Trump won the election, the Pentagon and Lockheed concluded negotiations on their ninth contract for F-35 fighter jets after 14 months of negotiation on the deal of more than $6.1 billion, Reuters reported.

Last week, Trump took a shot at Boeing via Twitter threatening to cancel its 747 Air Force One program. He claimed the total cost of a new 747 would be more than $4 billion. The company took a $1.4 billion hit to its market value.

CNBC's Jim Cramer said on "Squawk on the Street" on Monday that Trump's behavior is not typical of what previous presidents have done.

"I mean the president ... does he have the ability to say, 'Listen, we're going to take fewer product?' He does," He said. "Does he have the ability to say, 'Listen, we don't like these prices?' Historically, that's not what the president has done. People within the Pentagon have negotiated, but very high level."

Howard Rubel, Jefferies' managing director, told CNBC on Monday the cost of building a weapon defense program involves much more oversight than in the commercial world.

"I am sure there will be a list of how come things cost so much, and then you look at the engineering involved or the quality required to protect a solider. It will be an understanding of the balance versus the cost," he said.

Lockheed Martin's stock is up more than 19 percent this year.

—Reuters and CNBC's Steven Kopack contributed to this report.