Barclays (BARC.L), Royal Bank of Scotland (RBS), Citigroup (C), and JPMorgan (JPM) are among several banks that have been fined €1.07bn (£935m) by the European Commission for colluding on currency foreign exchange trading strategies.
The two settlement decisions are the result of an investigation into Barclays, the Royal Bank of Scotland (RBS), Citigroup, JPMorgan, UBS and MUFG Bank in relation to 11 currencies, including the euro, dollar, sterling and yen.
The investigation revealed that some individual traders in charge of foreign exchange spot trading for currencies on behalf of their associated banks exchanged sensitive information and trading plans.
Commissioner Margrethe Vestager, in charge of competition policy said: "Companies and people depend on banks to exchange money to carry out transactions in foreign countries".
Law firm Scott + Scott said it is preparing to launch a case on behalf of European clients after securing a $2.3 bn (£1.8bn) settlement in a United States class action suit related to foreign exchange market rigging.
Barclays, RBS and MUFG Bank, formerly the Bank of Tokyo-Mitsubishi, were fined for its part in the Forex-Essex Express cartel, the commission said.
UBS escaped a fine because it was the first to tell regulators about the collusion. The EC charged Credit Suisse Group past year. "We have since made significant control improvements", said a spokesperson for JPMorgan.
The banking industry has been hit with billions in fines worldwide over the last decade for rigging benchmarks used in many day-to-day financial transactions, and are now at risk of private lawsuits.
The fines for Barclays and RBS are covered by the two British banks' existing provisions and in line with expectations, according to Edward Firth, an analyst with Keefe, Bruyette & Woods in London.
"We are committed to ensuring integrity and compliance with the regulatory authorities in every jurisdiction in which we operate, and have taken a number of measures to prevent this occurring again".
Barclays and Citigroup declined to comment. They would sometimes agree to "stand down" or stop a trading activity to avoid interfering with another trader in the group. The body said the information exchange led to traders occasionally coordinating their strategies through online professional chat rooms.
The Essex Express cartel involving UBS, Barclays, RBS and MUFG, was given a 257.7 million Euro fine, with the penalty against Barclays the largest for this cartel at 94.2 million Euros.
According to Brussels, the banks formed those cartels in order to influence 11 different currencies, including the euro, USA dollar, pound sterling, Japanese yen, Swiss franc, and others.
Eight banks are the focus of yet another European Union probe looking at the trading of eurozone sovereign bonds from 2007 to 2012.
The EU regulator is also looking at "potential coordination in options trading" in the FX market, HSBC said in its annual report in February.