Switzerland's financial markets watchdog is investigating a number of the country's banks over potential manipulation of the £3 trillion-a-day foreign exchange market.
FINMA said it was probing several Swiss financial institutions, adding that "multiple banks around the world" are potentially implicated in what threatens to be another embarrassing scandal for the industry.
Financial markets are still battling to restore their reputation after the Libor rate-fixing scandal, which saw groups including Swiss bank UBS and Barclays in the UK pay hefty fines.
FINMA said it was "co-ordinating closely with authorities in other countries", but did not provide any further details of the investigation or name the banks involved.
UK regulator, the Financial Conduct Authority (FCA), declined to comment on whether it was involved in the investigation, saying only it was "aware of FINMA's statement".
Bloomberg News claimed in a report in June that dealers at banks shared information and used client orders to move benchmark currency rates.
The FCA said at the time it was reviewing the allegations.
Currency exchange rates are set on a daily basis by analysing actual trading volumes at leading banks during a short time window.
It is thought that traders could potentially influence exchange rates by pushing through large orders during the 60-second window to make a profit.
As with the Libor scandal, e ven a small movement in exchange rates could affect the value of investments worldwide, including pension funds.
According to the Bank for International Settlements, global foreign exchange activity rose to 5.3 trillion dollars (£3.3 trillion) a day this year, from 4 trillion dollars (£2.5 trillion) in 2010.
London accounts for the bulk of currency trading, with 41% of global turnover in the market, followed by the United States, which has a 19% share, Singapore with 5.7%, Japan with 5.6% and Hong Kong with 4.1%.