The Financial Industry Regulatory Authority, Wall Street's self-regulator, is looking into the activities of several traders who may have used sophisticated computer programs improperly, for example to manipulate the market by duping other investors in making trades, the paper said.
The newspaper quoted people familiar with the probe.
Credit Suisse may have granted traders access to its trading networks and its "dark pool", which the journal described as "a private, lightly regulated trading venue."
The bank has given some traders two months to find another trading partner, the paper said.
The probe is the latest headache for Switzerland's second-largest bank.
On Monday it pleaded guilty to helping Americans dodge taxes and agreed to pay a fine of $2.6 billion.