Investment banks are back in the firing line after European officials accused 13 of the industry's biggest firms of violating competition rules.
The European Commission said it suspected that the banks, including Barclays, Royal Bank of Scotland, UBS and Credit Suisse, blocked two exchanges from full trading in credit default swaps, a form of insurance that pays out when a company or country fails to honour a debt.
It said that Deutsche Boerse and the Chicago Mercantile Exchange attempted to break into the credit derivatives business between 2006 and 2009 but when they tried to obtain the necessary licences they were offered only "over-the-counter" trading rather than exchange trading.
The Commission said the banks acted collectively to shut out exchanges from the market because they feared that exchange trading would have reduced their own revenues from acting as intermediaries in the over-the-counter market.
The banks have historically traded the contracts "over-the-counter" - effectively among themselves - and released little information about trading prices to others who want to buy or sell them.
Joaquin Almunia, the Commission's vice-president in charge of competition policy, said the banks will have a chance to respond, but that if confirmed the matter "would constitute a serious breach of our competition rules".
He said: "It would be unacceptable if banks collectively blocked exchanges to protect their revenues from over-the-counter trading of credit derivatives.
"Over-the-counter trading is not only more expensive for investors than exchange trading, it is also prone to systemic risks."
The statement of objections also relates to the International Swaps and Derivatives Association (ISDA) and data service provider Markit.
The Commission alleges that when the exchanges turned to ISDA and Markit to obtain necessary licences for data and index benchmarks the banks instructed them to license only for "over-the-counter" trading purposes.