Think you're paying more for gas, electricity and soda? You could be right. And some people think big banks could be to blame.

From oil to electricity to metals, big banks, hedge funds and other "non-users" now own a large chunk of the world's resources.

That banks are allowed to own physical commodities -- as opposed to purely financial assets like futures contracts -- is a relatively new phenomenon.

In 2003, the Federal Reserve, which regulates investment banks, decided there was little risk to consumers or markets if the banks were allowed to own the commodities themselves.

But now critics are questioning whether that activity is distorting markets and driving up prices.

"These activities threaten to undermine the fundamental policy objectives that underlie the principle of separating banking from commerce," Saule Omarova, a law professor at the University of North Carolina at Chapel Hill's School of Law, wrote in a paper last year.

Omarova will be among four people testifying at a Senate hearing Tuesday on the impact banks are having on the commodities markets.

This comes on the heels of several reports of banks accused of hoarding commodities and driving up prices. In one case, JPMorgan (JPM) is expected to pay a massive fine for allegedly gaming the electricity market in California.

The bank would bid to deliver electricity to a utility the next day at a low price. When the next day came, JPMorgan would change its offer to a much higher price, assuring the power did not get bought, according to people familiar with the matter. Consumers would then have to compensate the bank for the cost of making the bid, under California's "make whole provision," which requires ratepayers to cover certain costs incurred by energy sellers.

It's not clear how JPMorgan made money on this arrangement, or if it was technically legal.

The government agency charged with policing electricity markets -- the Federal Energy Regulatory Commission -- declined to comment, and JPMorgan did not return an email.

FERC also recently fined British bank Barclays and Deutsche Bank for other improprieties involving the sale of power.

And The New York Times recently reported that Goldman Sachs (GS) is driving up the price of everything from soda cans to cars, by stockpiling its customers' aluminum in Detroit warehouses. By shuffling the metal between warehouses that it owns, Goldman is able to collect more rent for housing the metal, while complying with complex commodities laws.

Related: Is Goldman Sachs really raising the price of a Coke?

In addition to the Congressional hearings, the Federal Reserve is also revisiting the issue. Last Friday it issued a statement saying it "is reviewing the 2003 determination that certain commodity activities are complementary to financial activities and thus permissible for bank holding companies."

It's not just the owning of actual commodities that's drawing fire. Critics have long complained that investment money flowing into things such as oil futures is unduly driving up the price.

Bart Chilton, a member of the Commodity Futures Trading Commission, has said investor interest costs Americans $10 every time they fill up their gas tank. Current CFTC Chief Gary Gensler has long been a proponent of limiting the role investors can play in the oil markets, but attempts to implement those rules have faced court challenges.

These positions at CFTC are fairly new though. Under the Bush administration, the commissioner at the time repeatedly said there was no evidence investment money was driving up prices.

There are plenty of others that subscribe to this view. Even in cases where banks can own the commodity, like electricity, many think their involvement is a good thing.

While there may be some cases of banks behaving badly, on the whole, more players has meant lower and stable prices for consumers, they argue.

"From over 30 year of experience, I can tell you that the introduction of more buyers and sellers has been beneficial," said Susan Court, an analyst at SJC Energy Consultants specializing in FERC issues. "It makes for a more liquid market."