The European Commission fined four banks a total of €344 million (U.S. $389 million) for their participation in a trader-driven scheme to manipulate the foreign exchange spot market.

Through an investigation, the sixth such its conducted since 2013, the European Commission concluded traders from UBS, Barclays, NatWest (formerly RBS), HSBC, and Credit Suisse breached EU antitrust rules when they used an online professional chat room to exchange “sensitive information and trading plans, and occasionally coordinated their trading strategies” regarding nearly a dozen prominent currencies, the Commission said in a press release Thursday.

UBS, which reported the existence of the chat room and the cartel’s behavior to the European Commission, received immunity instead of potentially facing a €94 million (U.S. $106 million) penalty.

The fines “send a clear message that the Commission remains committed to ensure a sound and competitive financial sector that is essential for investment and growth,” Commissioner Margrethe Vestager said in the release. “Foreign exchange spot trading activities are one of the largest financial markets in the world. The collusive behavior of the five banks undermined the integrity of the financial sector at the expense of the European economy and consumers.”

The currencies at issue were so-called “G10” currencies that include the euro; British pound; Japanese yen; Swiss franc; U.S., Canadian, New Zealand, and Australian dollars; and Danish, Swedish, and Norwegian crowns.

The swapping of sensitive information and market strategies between traders from the five banks occurred from 2011-12 in a chat room called “Sterling Lads,” the Commission said. The use of the chat room “enabled the traders to make informed market decisions on whether and when to sell or buy the currencies they had in their portfolios, as opposed to a situation where traders acting independently from each other take an inherent risk in taking these decisions,” the Commission said. Traders would allegedly refrain from trading in certain foreign currencies to avoid interfering with another bank’s actions.

HSBC was fined €174.3 million (U.S. $197 million), Barclays €54.3 million (U.S. $61.4 million), and NatWest €32.5 million (U.S. $36.7 million). Those totals represented 10-15 percent reductions in recognition of cooperation with the investigation.

Credit Suisse, which the Commission said did not cooperate, was fined €83.3 million (U.S. $94.1 million). The bank received a 4 percent reduction on its penalty.

A spokesperson for UBS said, “This is a legacy matter where UBS was the first bank to disclose potential misconduct, and we are pleased the matter is resolved.”

A NatWest spokesperson said the bank is “pleased” to have settled the matter, which regarded “serious misconduct that took place in a single chatroom, and that involved a former employee of the bank, around a decade ago. It follows the settlements reached with U.K., U.S., and European authorities on similar issues. Our culture and controls have changed fundamentally during the past 10 years, and this kind of behavior has no place at the bank we are today.”

Representatives of Credit Suisse, Barclays, and HSBC declined to comment on the Commission’s action.

In 2019, as part of the same investigation into foreign currency manipulation, the European Commission levied a total of €811.2 million (then-U.S. $907 million) in fines on Barclays, RBS, Citigroup, and JPMorgan for their participation in the so-called “Three-Way Banana Split” cartel that operated from 2007-13. At the same time, the Commission also penalized Barclays, RBS, and MUFG Bank €257.68 million (then-U.S. $288 million) for their roles in the “Essex Express” cartel that operated from 2009-12.

UBS was involved in both cartels but not fined because it revealed their existence to the Commission.

Earlier this year, the European Commission concluded an investigation into a separate forex trading scheme when it fined three banks—Nomura, UBS, and UniCredit—a total of €371 million (then-U.S. $453 million) for their participation in a cartel scheme through a group of traders. That scheme also involved four other banks.

In that case, NatWest received immunity for revealing the existence of the cartel. Violations by Bank of America and Natixis occurred outside the limitation period for imposing fines, while Portigon, the legal and economic successor of WestLB, had its penalty reduced to zero after not producing any net turnover in the previous business year.