“It’s more than the extent of the violation,” he said. “It’s the almost comedic quality of the violation.”

A spokeswoman for the S.E.C. did not respond to a request for comment.

Start-ups have raised more than $3 billion this year from investors through coin offerings. Most start-ups say the coins they are selling will be useful as a method of payment in the online services they are building.

Coin offerings generally happen without the involvement of financial institutions or regulators because investors pay for the coins using Bitcoin and other virtual currencies, which can be sent outside the traditional financial system.

Regulators in China and South Korea have recently banned such offerings outright.

In the United States, the S.E.C. has brought one case against a small fraudulent coin offering. The agency has also warned that at least some coins being sold could be considered securities, and would be in violation of securities law if not registered with the authorities — and few are.

But Mr. Grundfest, who is also a co-director of the Rock Center for Corporate Governance, said the continuing flow of new coin offerings showed that the warnings were not nearly enough.