BRUSSELS (AFP) ― EU investigators accused 13 top banks including Barclays, Deutsche Bank and Goldman Sachs on Monday of colluding over derivatives trading, in a new move to tighten banking standards.

A preliminary investigation by the Commission showed that banks worked together to exclude exchanges from the derivatives market.

This was allegedly because they feared involvement by the exchanges would cut into their huge profits from over-the-counter trading.

Some aspects of derivatives trading have been blamed for exacerbating the financial crisis.

The EU’s Competition Commissioner Joaquin Almunia said that the banks now had the chance to respond to the detailed accusations.

He said that they could face fines if the charges were confirmed once the investigation had been completed.

“If it is confirmed that banks collectively blocked exchanges from the derivatives market, the Commission could decide to impose sanctions,” Almunia said at a press briefing.

“Exchange trading of credit derivatives improves market transparency and stability,” he said.

Collusion between banks to prevent this type of trading would be “a serious breach of our competition rules,” he said.

Almunia declined to give an estimate of the size of possible fines on the banks but he said the CDS market at the moment was worth about 10 trillion euros ($13 trillion).

The collapse of U.S. investment bank Lehman Brothers in 2008 “showed how derivatives trading are able to destabilize the entire financial system,” Almunia said.

The EU investigation began in 2011 and has focused on claims that the Deutsche Boerse stock market and the Chicago Mercantile Exchange were excluded from the derivatives market between 2006 and 2009 when the crisis reached its peak.

It said the two exchanges decided to turn to the International Swaps and Derivatives Association and data service provider Markit to obtain the necessary licenses but were turned down because the banks had prevented them from doing so.

The 13 European and U.S. banks targeted are: Bank of America Merrill Lynch, Barclays, Bear Stearns, BNP Paribas, Citigroup, Credit Suisse, Deutsche Bank, Goldman Sachs, HSBC, JPMorgan, Morgan Stanley, Royal Bank of Scotland and UBS.

Four other banks that had been involved in the investigation ― Commerzbank, Societe Generale, Credit Agricole and Wells Fargo ― have been excluded because of a lack of evidence.