WASHINGTON—Federal regulators proposed a bevy of new requirements for special-purpose acquisition companies, or SPACs, and their takeover targets amid widespread concern that the vehicles skirt important investor protections.

The Securities and Exchange Commission advanced a set of rules Wednesday that, if implemented, would make it harder for SPACs to raise money from investors and execute mergers. Its goal is to force the vehicles to meet similar regulatory standards as initial public offerings, though critics accused the agency of aiming to end their use altogether.