EU antitrust regulators on Thursday fined Barclays (BARC.L), Credit Suisse (CSGN.S), HSBC (HSBA.L) and NatWest (NWG.L) 344 million euros ($390 million) for foreign exchange market rigging, closing a key chapter in a high-profile investigation. UBS (UBSG.S) avoided a 94 million euro fine by alerting the European Commission to the cartel, which was set up via a chatroom known as "Sterling Lads". HSBC received the largest fine at 174.3 million euros, followed by Credit Suisse at 83.3 million euros, Barclays at 54.3 million and RBS at 32.5 million. Barclays, HSBC and RBS - known as NatWest since a rebranding - admitted wrongdoing in return for a reduced penalty. NatWest said the misconduct took place about a decade ago in a single chatroom, involved a former employee and that its culture and controls had since fundamentally changed. UBS said it had been the first bank to disclose potential misconduct and was pleased the matter was resolved. Barclays, Credit Suisse and HSBC declined to comment. Some of the world"s biggest banks have been fined more than $11 billion collectively by U.S. and European regulators since allegations first surfaced around 2013 that dealers were rigging the world"s largest financial market. Dozens of traders were suspended or fired. The latest investigation focused on foreign exchange (forex) spot trading of G10 currencies, the most liquid and traded currencies in the world, which include the U.S. dollar, pound and euro. Traders exchanged sensitive information and trading plans and sometimes coordinated strategies through the online chatroom, the Commission said. The EU has already sanctioned some of the same banks over similar conduct in 2019 in a settlement featuring chatrooms called "Three Way Banana Split", "Only Marge","Essex Express" and "Semi Grumpy Old Men". "Today we complete our sixth cartel investigation in the financial sector since 2013 and conclude the third leg of our investigation into the foreign exchange spot trading market," EU antitrust chief Margrethe Vestager said in a statement. She said the collusive behaviour of the five banks undermined the integrity of the financial sector at the expense of the European economy and consumers. Barclays, Citigroup (C.N), JP Morgan (JPM.N), MUFG and RBS were fined a combined 1.07 billion euros in May 2019 by the EU antitrust authorities for manipulating the foreign exchange market via two cartels, between 2007 to 2013 for one group and between 2009 to 2012 for the other. ($1 = 0.8828 euros)