Competition authorities of the European Union are investigating the activities of nine of the world's biggest banks over the market for credit default swaps.
The banks include Barclays, Goldman Sachs, Deutsche Bank and Citigroup, the BBC reports.
The other five banks involved are Bank of America, Credit Suisse, JP Morgan Chase, Morgan Stanley and UBS.
Credit default swaps (CDS) are a form of insurance policy taken out on financial instruments, such as bonds, in case they lose value.
The European Commission said it is investigating whether the nine big investment banks received special treatment from the clearing house ICE Clear Europe, and were therefore only giving their business to ICE.
During the height of the financial crisis there were concerns that speculation in CDS for bonds was driving down prices and fuelling market panic.
The value of CDS are said to be in the region of $US28 trillion, dwarfing the worth of the instruments they are based on.
As well as providing insurance against a bond going bad, they are used for speculation, with banks and hedge funds trading in the swaps to make money without actually owning the underlying bonds.