BRUSSELS—European antitrust authorities are moving soon to bring a case against some of the world's largest banks alleging collusion in the $27 trillion market for credit derivatives, people familiar with the investigation said.

The probe by the European Commission involves 16 financial groups. It focuses on whether they sought to stifle competition from exchanges in the market for credit-default swaps, which pay out when a country or a company defaults on its debts.

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