The case is a reminder of how much of Musk’s wealth comes from taxpayers. His companies have government contracts worth hundreds of millions of dollars a year.

The State Department had been in talks with Elon Musk's Tesla company to buy armored electric vehicles, but the plans have been put on hold by the Trump administration after reports emerged about a potential $400-million purchase.

That's according to a public State Department procurement document. It comes as ethics experts raise conflict of interest questions about the chief executive of Tesla, Elon Musk, who is a close adviser to President Trump.