The mayor has been an enthusiastic proponent of MiamiCoin, a privately-owned cryptocurrency.
The ability to coordinate outside of government control could be a massive boon for oppressed or dissident groups.
Some crypto skeptics say that regulating the digital coin is a mistake since it would provide legitimacy to the industry.
Toomey advocated instituting consumer protections and disclosure requirements in the crypto industry.
CFTC Chairman Rostin Behnam called on Congress to institute robust disclosure regimes and barriers against conflicts of interest.