Deutsche Bank, HSBC and Bank of Nova Scotia have been accused of attempting to rig the price of silver, in a lawsuit filed in the US.
The plaintiff alleges the banks, which set the price of silver each day, abused their position in the market.
Deutsche Bank and HSBC have not commented on the filing, while Bank of Nova Scotia told Bloomberg news agency it would "vigorously defend" itself.
The lawsuit follows similar filings in the gold price-fixing market.
Earlier this year, Barclays Bank was fined £26m ($44m) by UK regulators after one of its traders was discovered attempting to fix the price of gold.
Investor Scott Nicholson from Washington said in the filing against the three banks for price-fixing: "The extreme level of secrecy creates an environment that is ripe for manipulation.