If you're a U.S.–based hedge fund operating out of a post office box in the Cayman Islands, Gary Gensler, chairman of the Commodity Futures Trading Commission, has a message: Get ready for more oversight.

At a meeting on July 12, a divided CFTC approved final guidance covering cross-border swap transactions, a crucial element of financial reform. But questions remain about exemptions, enforcement, and whether the agency may have violated the Administrative Procedure Act in rolling out the guidance.