Elon Musk, CEO of Telsa, says on Twitter: BlackRock helps sellers in the open

Elon Musk, CEO of Tesla, accused major fund managers such as BlackRock of feeding short sellers, a group of investors he criticized from his Twitter account.

Musk tweets: The big funds can and go because they suffer a net loss. Index managers such as Blackrock pocket are making excessive profits on short-term loans while claiming to charge low rates for "passive" tracking of the index.

CNBC contacted BlackRock to comment on Musk's allegations, but did not hear from the company.

Fund managers reduced management fees on certain products due to increased competition in the sector. Fidelity Investments announced last month the launch of two index funds free of charge. Vanguard announced in July that investors using its online brokerage platform could trade non-commissioned exchange-traded funds.

At the same time, fund managers have developed their activities in the securities lending sector, a process that involves temporarily transferring ownership of shares or bonds to another party, such as short sellers. Companies receive fees in exchange for loaning their assets.

Lending securities is a lucrative business, according to an article published by the Financial Times in April. The newspaper, citing a regulatory filing, said BlackRock had generated $ 597 million in revenue last year through securities lending.

Musk criticized this practice, claiming that there was "no rational basis" for long-term shareholders to engage in this activity. He claimed that it "diluted the shareholding" and gave short sellers "a strong incentive to attack society by any means possible".

Musk Tweets: There is no rational reason for a long holder to lend his shares to shorts, as this dilutes the shareholder base and makes the broker highly motivated to attack the company by any means, including regulators

The billionaire CEO also said that many small investors in passive index funds did not know that their holdings were being lent to short sellers.

Some called Musk not to understand how markets work. Several people who responded to his messages pointed out that investors who believe that Tesla would be interested in lending their shares to short sellers.

"Longs can earn a return while some fools bet against stocks that they think will increase – anything that makes them lend money," wrote Dave Lauer, who studies the structure and volatility of the markets. "Long" refers to investors who buy an asset in the hope that the price will increase.

Dave Lauer tweets: It's crazy. Long can yield returns, while some idiots are betting on stocks that they think will go up. There is interest in long lending.

Musk has been a virulent critic of short sellers, calling them once "jerks who want us dead" and accusing them of spreading "negative propaganda" against Telsa. On Thursday, he also scoffed at the Securities and Exchange Commission in calling it "the short sellers' enrichment commission" and said what sellers are doing "should be illegal." ".

Tesla has been a prime target for short sellers because of its rapid liquidity consumption and difficulty generating profits. Jim Chanos of Kynikos Associates and David Einhorn of Greenlight Capital Fund are among the equity brokers of the company.