Barclays is set to be fined $70 million (£49m) in the US after misleading investors over its 'dark pool' trading, the New York Attorney General's office has said.
The Attorney General has accused the bank of not making it clear to investors that its high-frequency traders operated on the private platform, which allows the value of trades to be kept secret.
Barclays is also expected to admit that it broke the law, and will install independent monitors to review its trading operations.
Credit Suisse will also be fined $84.3m over its dark pool trading. But whereas Barclays is likely to admit wrongdoing, Credit Suisse isn't expected to confirm or deny any wrongdoing.
Eric Schneiderman, the New York attorney general, said: "These cases mark the first major victory in the fight against fraud in dark pool trading that began when we first sued Barclays.
"We will continue to take the fight to those who aim to rig the system and those who look the other way."
Andrew Ceresney, director of the Securities and Exchange Commissions (SEC)'s enforcement department, said: "Dark pools have a significant role in today's equity marketplace, and the firms that run these venues must ensure that they do not make misstatements to subscribers about their material operations.''