The U.S. securities regulator on Monday issued accounting guidance for special purpose acquisition companies, or SPACs, which called into question whether warrants issued by hundreds of SPACs could be considered equity instruments.

The guidance suggests that many SPACs may potentially have to refile their financial statements to account for the warrants as a liability.

Last week, an official with the U.S. Securities and Exchange Commission (SEC) had said the agency was reviewing filings and seeking clearer disclosures for SPACs, and detailed concerns around fees, conflicts and sponsor compensation.

SPACs are listed shell companies that raise funds to acquire a private company with the purpose of taking it public, allowing such targets to sidestep a traditional initial public offering.

The announcement is the latest move by SEC to clamp down on Wall Street’s biggest gold rush in recent years, with SPACs raising a record $170 billion so far this year and surpassing last year’s total of $157 billion, Refinitiv data showed.

Last month, Reuters had reported that SEC opened an inquiry into Wall Street’s blank-check acquisition frenzy and is seeking information on how underwriters are managing the risks involved.