The US Securities and Exchange Commission on Thursday issued an investor alert warning that firms offering crypto asset securities may not be complying with US laws.
Unregistered offerings of such securities may not provide important data, including audited financial statements, for informed decision making, the SEC said.
The securities watchdog has been cracking down on the crypto industry, which its chair has called a "Wild West" riddled with misconduct. Its efforts gathered pace after November's collapse of Sam Bankman-Fried's cryptocurrency exchange FTX.
Crypto exchange Coinbase announced on Wednesday that it had received a Wells notice - a formal declaration that SEC staff intend to recommend an enforcement action.
In its investor alert, the SEC also warned investors about "proof of reserves" services offered by some crypto exchanges that are supposed to let users verify that an exchange has enough assets to back customers' holdings.
"Crypto asset entities might use these in lieu of audited financial statements in order to obscure and confuse customers about the safety of their assets," the SEC said.