(Reuters) – U.S. On Wednesday, Senator Elizabeth Warren joined three other Senate Democrats in writing to the top SPAC dealmakers. They expressed concern over claims that SPAC insiders are exploiting regulatory loopholes against retail investors.

SPACs (special purpose acquisition companies) are shell corporations that seek to raise capital through an initial public offering in order to merge a private company.

They wanted information about how SPACs raised funds, the compensation of executives and how that was related to stock performance.

The letters were signed by Senators Elizabeth Warren (Sherrod Brown), Tina Smith (Tina Smith) and Chris Van Hollen. They asked for information regarding your SPAC use to determine what regulatory or Congressional actions may be required to better protect investors.

The letters were sent to six SPAC investors, including Cantor Fitzgerald’s Chief Executive Officer Howard Lutnick, former Citigroup (NYSE:) banker Michael Klein, casino mogul and Houston Rockets owner Tilman Fertitta and veteran investor Chamath Palihapitiya.

David Hamamoto (who led the SPAC which merged with EV manufacturer Lordstown Motors Corp) and Stephen Girsky, former vice chairman of General Motors (NYSE.:) were also included in the letters.

Following the scrutiny of the United States regulators earlier in the year, it seems that the market for blank checks, which was seeing dealmaking activities at an explosive pace, is now somewhat dead.

U.S. Securities and Exchange Commission are also looking into such acquisition vehicles and seeking more disclosures.