Kimbal Musk, the brother of Tesla CEO Elon Musk, has been offloading shares of Tesla in recent months just as the stock has made a massive retreat from all-time highs. The electric vehicle maker, however briefly, had been among the select group of trillion-dollar companies following the stock’s post-U.S. presidential election surge.

Investors are questioning the tech billionaire's involvement in Trump's administration, while shares in his Tesla electric-car company plummet.

Tesla's reported letter comes after unpredictable Trump trade policy moves that have unsettled businesses and markets.