After a financial reporter compared one big bank to a “great vampire squid” a few years ago, a top lawmaker now wants to block megabank activities in commodities to stymie “the tentacles of this octopus.”

Sen. Sherrod Brown, D-Ohio, used his sea monster metaphor recently to express his concern that bank involvement in electricity sales, oil transport, metals warehousing and other commercial businesses creates risks running from illegal insider trading to destabilizing the financial system.

“I want banks to do mortgages, not oil transport,” Brown was quoted in the Financial Times. “The tentacles of this octopus could put the stability of the financial system at risk.”

Brown referred specifically to a $410 million fine agreed to by JP Morgan Chase last week to settle government allegations of manipulating the electricity markets in California and Michigan.