The top U.S. derivatives regulator may dwindle to just two voting commissioners and struggle to approve new rules unless the White House and Senate can overcome political hurdles to fill the vacancies by the end of the year.

The Commodity Futures Trading Commission, which is designed to have five members regulate trading by banks including Goldman Sachs Group and JPMorgan Chase, could instead have only one Democrat and one Republican early next year. The split would probably delay votes on contentious Dodd-Frank Act regulations.