The early-stage Securities and Exchange Commission probe is focused on an uptick in sales of pre-IPO shares of buzzy tech startups by middlemen at a time when valuations for those companies have climbed higher and higher, according to anonymous sources cited in a new report from The Wall Street Journal. The SEC is also investigating the sale of employee-owned shares of private companies in transactions that are sometimes forbidden by those companies and can violate the Dodd-Frank Act.

According to WSJ, the SEC probe includes one hedge fund manager who, earlier this year, tried lining up investors to support a $100 million fund to invest in Uber stock. The manager, Artist Capital’s Jonathan Sands, told investors he was getting the stock “directly” from Uber until the ride-hailing startup’s lawyers learned of his deception and asked him to stop.

The investigation comes at a time when funding for private tech companies is piling up, sending the pre-IPO valuations of tech startups like the $50 billion Uber sky high. Last year, venture capital funding for tech startups increased 25%, to nearly $65 billion.

Last month, the SEC announced an enforcement action against Silicon Valley startup Sand Hill Exchange for selling security-based swaps contracts to investors outside a national securities exchange and without proper registration statements. Sand Hill settled the SEC’s charges and agreed to pay a $20,000 penalty.