New York CNN Business  — 

Senator Elizabeth Warren and three other Democratic lawmakers have sent an open letter to the executives behind popular SPACs, raising concerns about the potential for insiders to exploit regulatory gaps at the expense of everyday investors.

“We seek information about your use of SPACs in order to understand what sort of Congressional or regulatory action may be necessary to better protect investors and market integrity and ensure a fair, orderly, and efficient marketplace,” the senators wrote Wednesday. “We are concerned about the misaligned incentives between SPACs’ creators and early investors on the one hand, and retail investors on the other.”

SPACs, or special purpose acquisition companies, have grown in popularity lately. As a publicly listed shell company that hunts for an acquisition, SPACs allow a private firm to bypass the typically lengthy and expensive process of a traditional initial public offering.

Although these kinds of deals were once frowned upon, SPACs have become all the rage, with major companies including Virgin Galactic (SPCE), DraftKings and Playboy all going public this way. But the uncertainty surrounding these deals has prompted UBS (UBS), a major player in the blank-check boom, to ban its financial advisers from pitching SPAC stocks to wealth management clients.

The senators’ letter was sent to Howard Lutnick, the CEO of Cantor Fitzgerald, Tilman Fertitta, the CEO of Fertitta Entertainment and Chamath Palihapitiya, CEO of the Social and Capital Partnership, among others.

In addition to Warren, the other senators who signed the letter include Sherrod Brown, Tina Smith and Chris Van Hollen. They said that SPACs might be ripe for “industry insiders” to “take advantage of retail investors” and that people backing SPACs, such as sponsors, might have “incentives to quickly strike merger deals, regardless of the quality of the deal or of the company to be acquired.”

The senators have requested the information be provided by October 8.

—CNN Business’ Matt Egan contributed to this report.