Amid new regulatory scrutiny, investors are reportedly “cooling to one of the hottest bets on Wall Street,” cutting the flow of new SPAC issues “to a trickle while share prices tumble.” This according to a recent article in The Wall Street Journal.

SPACs—special purpose companies formed for the purposes of merging with a business and taking it public—have reportedly raised approximately $100 billion so far this year compared to last year’s record $83.4 billion, “which itself was more than the amount raised in the nearly 30-year history of these blank-check companies,” the article reports.

According to the article, ”SPACs have proliferated as a faster alternative to initial public offerings, giving  many risky, young companies an opening to raise large sums of money and sell shares to the public.” It adds, however, that “critical comments from regulators appear to be scaring off some investors and new offerings,” with the slowdown coming as other assets (i.e. stocks and cryptocurrencies) are “at or near records.”

Specifically, in recent weeks the SEC questioned the optimistic revenue projections used by startups that are merging with SPACs. A warning from the regulatory agency could require some SPACs to restate their financial results and “put the brakes on some new offerings.”

The article reports that regulators have been concerned about the SPAC frenzy that has burned some investors due to their unusual structure: “They need to find a company to buy, usually within two years, or give their cash back to investors.” It notes that there are currently about 430 SPACs seeking private firms to take public.