The U.S. Securities and Exchange Commission has issued a warning to celebrities on a hot new digital investment, initial coin offerings. The SEC said they may be breaking the law if they don’t disclose paid endorsement of the ICOs.

Boxing champion Floyd Mayweather, rapper Ghostface Killah, and celebutant Paris Hilton are among the prominent names who have gotten behind recent ICOs, and that has apparently caught the eye of the SEC Enforcement Division and Office of Compliance Inspections and Examinations.

The SEC has issued a public memo warning of consequences. “Celebrities and others are using social media networks to encourage the public to purchase stocks and other investments,” said the memo. “These endorsements may be unlawful if they do not disclose the nature, source, and amount of any compensation paid, directly or indirectly, by the company in exchange for the endorsement.”

Mayweather has been a particularly zealous advocate for ICOs. His endorsement for a blockchain prediction market, Stox, helped push it to $30 million raised in its ICO. Mayweather boasted on Instagram that he was  “gonna make a $hit t$n of money on August 2nd on the Stox.com ICO.” Ironically, as a U.S. citizen, Mayweather was not eligible to participate directly in the purchase, which was not directly open to U.S. citizens.

ICO investments have now topped $3 billion this year, dwarfing the funds raised through traditional venture capital and bank loans.  The SEC has indicated that many of the tokens sold are, in fact, securities. That makes them subject to the same laws as any public stock offering if the company is based in the U.S. or sells its tokens to this market.

A failure to disclose any paid endorsement of an ICO is a violation of the anti-touting provisions of the federal securities laws, according to the SEC. Violations could be subject to laws that govern participation in an unregistered offer and sale of securities, and for acting as an unregistered broker.