Five banks have been fined a total of €1.07bn (£935m) by the European Commission for forming illegal cartels to rig the foreign exchange market.
Four banks in the “Banana Split” cartel – Barclays, RBS, Citigroup and JP Morgan – were fined €811m in all.
Another three banks in the “Essex Express” cartel – Barclays, RBS and MUFG – were fined €258m.
A sixth bank, UBS, was excused financial penalties for revealing the cartels’ existence.
The European Commission said the market-rigging took place from 2007 to 2013.
Competition Commissioner Margrethe Vestager said the banks’ behaviour “undermined the integrity of the sector at the expense of the European economy and consumers”.