The European Commission has fined HSBC, JPMorgan and Credit Agricole a total of 485 million euro (£412 million) for their role as part of a cartel that conspired to rig interest rate derivatives.
The EU's antitrust watchdog said the banks colluded on manipulating euro interest rate derivative pricing elements and exchanged sensitive information "to distort the normal course of pricing".
HSBC was fined 33.6 million euro (£28.6 million), Credit Agricole 114.7 million euro (£97.6 million) and JPMorgan 337.2 million euro (£287 million) for breaching regulation.
Commissioner Margrethe Vestager said: "A sound and competitive financial sector is essential for investment and growth. Banks have to respect EU competition rules just like any other company operating in the Single Market."
The case covers manipulation of financial contracts linked to the benchmark Euribor interest rate in the period between 2005 and 2008.
In 2013, antitrust regulators reached a settlement with Barclays, Deutsche Bank, Royal Bank of Scotland and Societe Generale as part of the same case.
The Commission added: "The participating traders of the banks were in regular contact through corporate chat-rooms or instant messaging services.
"The traders' aim was to distort the normal course of pricing components for euro interest rate derivatives.
"They did this by telling each other their desired or intended Euribor submissions and by exchanging sensitive information on their trading positions or on their trading or pricing strategies."
For its part, HSBC said it is considering its legal options and denied that it belonged to a cartel.
" The European Commission's decision relates to allegations of Euribor manipulation and related purported conduct during the course of one month in early 2007. We believe we did not participate in an anti-competitive cartel. We are reviewing the European Commission's decision and considering our legal options," the bank said.
JP Morgan also said it was gearing up for potential legal action.
"We have co-operated fully with the European Commission throughout its five-year investigation. We did not engage in any wrongdoing with respect to the Euribor benchmark. We will continue to vigorously defend our position against these allegations, including through possible appeals to the European courts."