Lockheed Martin CEO Marillyn Hewson is seeing what Donald Trump may be prepared to do to get military procurement costs down.

“Based on the tremendous cost and cost overruns of the Lockheed Martin F-35, I have asked Boeing to price-out a comparable F-18 Super Hornet!” Trump writes on Twitter.

Earlier in the week, Trump met with Hewson. “We’re just beginning, it’s a dance,” Trump told reporters after that meeting.

The latest tweet sent Lockheed shares into a tailspin. According to CNBC, they fell about two percent, losing an estimated $1.2 billion of market value.

Earlier this month, Trump targeted the company because of the sky-high costs of the program.

“The F-35 program and cost is out of control,” Trump wrote on Twitter about Lockheed Martin’s program.

It has an estimated cost of $1.45 trillion over the next 50 years. In 2009, the cost of the program was estimated at $900 million.