The Commodity Futures Trading Commision (CFTC) is investigating a large number of trades in energy and metal markets to determine whether traders illegally used over-the-counter swaps markets to trade futures.

According to Reuters, the CFTC has asked the largest banks for data going back to 2010 as part of the agency’s probe. The CFTC’s inquiry, which is known as a “special call”, was into exchanges of futures for swaps (EFS).

Up until last year, a large amount of off-exchange energy and metal derivatives were traded as EFS via the ClearPort mechanism of CME Group Inc. In the ClearPort system transaction, the swap existed for a mere fraction of a second, instantly converting to a futures contract after execution.

After 2008’s Wall Street meltdown, there was a spike in EFS trades, as the oil industry adopted clearing as a way to minimize counterparty risk in over-the-counter trades.

However, under the Dodd-Frank Act, the transactions are deemed as swaps, even if it is just for a solitary moment. As a result, EFS trading has been diminished.

One industry executive told Reuters, “In a way they’re fighting last year’s war.”

Many industry participants worry that the request for more data is a sign that the CFTC is not comfortable with the industry’s brisk move to convert hundreds of energy, metals and agricultural swap contracts into futures, in order to avoid new regulations.