Elon Musk says these shareholder advisors 'effectively control the stock market' and have too much power

• Elon Musk said proxy advisory firms ISS and Glass Lewis have too much influence. 
• "ISS and Glass Lewis effectively control the stock market," he tweeted late Monday. 
• Musk added that many investors hold stocks in passive index funds, meaning shareholder voting decisions are "outsourced" to the advisories.

Elon Musk said proxy advisory firms Institutional Shareholders Services and Glass Lewis have too much sway over the stock market. 

The firms offer recommendations to shareholders on how to they should vote on management proposals at company meetings.