The Commodity Futures Trading Commission is conducting a broad inquiry into the legitimacy of more than 1 million energy and metals transactions by the biggest traders in commodities markets over the past two years.

The CFTC has issued a “special call” asking Wall Street banks and other traders to provide documents that would prove recent derivatives transactions known as “exchanges of futures for swaps” were legal, the Financial Times reported Tuesday. Lawyers at the agency’s enforcement division are also checking the trades for possible violations.

Leading banks that have received document requests include JPMorgan Chase, Goldman Sachs and Citigroup. They declined to comment.

“They are looking at a huge amount of trading,” an industry lawyer said.

The CFTC action shows how authorities are clamping down on previously unregulated derivatives dealing in markets from commodities to interest rates. The CFTC this week is set to impose new trading rules for over-the-counter markets, even as the Group of 20 industrial countries seeks to shift more derivatives to electronic platforms.

The current probe centers on whether large traders and market-makers used unregulated over-the-counter swaps markets to trade what were in fact futures, strictly regulated contracts that are effectively identical to swaps.

Trading futures off an exchange is illegal, and regulators are concerned that traders may have used these deals, known as EFSs, to agree on prices that did not reflect the market.

“They’ve made information requests to everybody that’s ever traded an EFS. They’re saying, ‘prove to us that the swap was legitimate’,” a recipient of a CFTC document request told the Financial Times.