A Fed spokeswoman, Barbara Hagenbaugh, provided the following statement: “The Federal Reserve regularly monitors the commodity activities of supervised firms and is reviewing the 2003 determination that certain commodity activities are complementary to financial activities and thus permissible for bank holding companies.”

Senator Sherrod Brown, who is sponsoring Congressional hearings on Tuesday on Wall Street’s ownership of warehouses, pipelines and other commodity-related assets, says he hopes the Fed reins in the banks.

“Banks should be banks, not oil companies,” said Mr. Brown, Democrat of Ohio. “They should make loans, not manipulate the markets to drive up prices for manufacturers and expose our entire financial system to undue risk.”

Next Up: Copper

As Goldman has benefited from its wildly lucrative foray into the aluminum market, JPMorgan has been moving ahead with plans to establish its own profit center involving an even more crucial metal: copper, an industrial commodity that is so widely used in homes, electronics, cars and other products that many economists track it as a barometer for the global economy.

In 2010, JPMorgan quietly embarked on a huge buying spree in the copper market. Within weeks — by the time it had been identified as the mystery buyer — the bank had amassed $1.5 billion in copper, more than half of the available amount held in all of the warehouses on the exchange. Copper prices spiked in response.

At the same time, JPMorgan, which also controls metal warehouses, began seeking approval of a plan that would ultimately allow it, Goldman Sachs and BlackRock, a large money management firm, to buy 80 percent of the copper available on the market on behalf of investors and hold it in warehouses. The firms have told regulators that these stockpiles, which would be used to back new copper exchange-traded funds, would not affect copper prices. But manufacturers and copper wholesalers warned that the arrangement would squeeze the market and send prices soaring. They asked the S.E.C. to reject the proposal.

After an intensive lobbying campaign by the banks, Mary L. Schapiro, the S.E.C.'s chairwoman, approved the new copper funds last December, during her final days in office. S.E.C. officials said they believed the funds would track the price of copper, not propel it, and concurred with the firms’ contention — disputed by some economists — that reducing the amount of copper on the market would not drive up prices.