It’s rulemaking season over at the U.S. Securities and Exchange Commission. Which means lobbying groups and think tanks focused on cryptocurrency are on high alert.

Washington, D.C.-based advocacy group Coin Center is directing attention to the SEC’s proposed redefinition of the term “exchange” within the Securities Exchange Act to “include systems that offer the use of non-firm trading interest and communications protocols to bring together buyers and sellers of securities.”

In a comment letter to the agency today, Coin Center calls the rule “unconstitutional.”

A change to a definition within a law first drafted in 1934 may seem ho-hum, especially when placed in the most arcane language imaginable, but the consequences are real. Entities that fall under that definition would be required to register with the SEC. According to research director Peter Van Valkenburgh, that would include “anyone writing or distributing [decentralized exchange] software”—even though the agency never mentions DeFi or crypto.

Decentralized finance (DeFi) refers to a group of blockchain-based technologies that allow people to transact on a peer-to-peer basis, i.e., without an intermediary. Within DeFi, decentralized exchanges let people trade tokens without relying on a third party to ever take custody of the assets being traded.

In Van Valkenburgh’s view, the…