Swiss competition regulator Weko has opened a probe into several well-known banking giants amid suspicion that their traders worked together to fix foreign exchange rates.
RBS, Barclays, UBS, JPMorgan, Citigroup, Credit Suisse, Julius Baer and Zurich Cantonal Bank are all subject to Weko's fresh investigation.
Regulators across the world, including in New York, London and Hong Kong, are investigating allegations of manipulation in the £3tn daily currency market.
Weko claimed "evidence exists" that the banks under its investigation "colluded to manipulate exchange rates in foreign currency trades". Its investigation is not in conjunction with other regulators.
"Credit Suisse AG was astonished to note the allegations made by the Swiss Competition Commission in the press release issued today," said a statement from the bank.
"Credit Suisse AG was not the subject of the preliminary investigation carried out by the Competition Commission into various banks.
"The press release contains incorrect references to Credit Suisse AG and these allegations are both inappropriate and harmful to our reputation. Credit Suisse AG will cooperate fully with the authorities in this matter."
Julius Baer said its own internal investigation showed "no indication whatsoever" of market abuse, but that it would co-operate with Weko's probe.
An RBS spokeswoman said the bank would fully co-operate with the Weko investigation.
JPMorgan and Zurich Cantonal Bank had not yet responded to IBTimes UK's request for comment.
UBS, Barclays and Citigroup all declined to comment.