The European Commission's antitrust watchdog said it suspects that HSBC, JPMorgan and Credit Agricole worked together in an interest-rate fixing cartel.
It issued the banks with what is called a "Statement of Objections", a document in which the Commission lists the suspected violations of EU rules. The institutions accused can then examine the case against them and respond in writing or at an oral hearing.
HSBC, JPMorgan and Credit Agricole are suspected of manipulating the Euro Interbank Offered Rate (Euribor), a benchmark interest rate that informs the pricing of financial products tied to it. These products are known as interest rate derivatives.
If the competition rules are found to have been breached, the Commission has the power to extract a fine worth up to 10% of the global turnover of each business.
"The Commission has concerns that the three banks may have taken part in a collusive scheme which aimed at distorting the normal course of pricing components for euro interest rate derivatives," said a statement from the EU.
JPMorgan and Credit Agricole had not replied to IBTimes UK's request for comment at the time of publishing.
"We intend to defend ourselves vigorously," said a spokesman for HSBC.
In December 2013, the EU Commission fined eight banks a combined €1.71bn (£1.4bn, $2.34bn) for operating in interest rate fixing cartels.
Most of the banks involved settled with the Commission, but three did not – HSBC, Credit Agricole and JPMorgan.
The Commission said its Statement of Objections issued to the trio does not prejudge the result of its ongoing investigation.