Switzerland's competition commission WEKO said on Monday it had opened an investigation into several Swiss, British and US banks over potential collusion to manipulate foreign exchange rates.
WEKO said it is investigating UBS, Credit Suisse, Zuercher Kantonalbank, Julius Baer, JP Morgan, Citigroup, Barclays and Royal Bank of Scotland.
A spokeswoman for Edinburgh-based RBS said: "We will co-operate fully with any regulatory investigation."
There are already investigations running in the United States, Britain, Germany and Singapore into allegations of collusion and manipulation by traders.
There are concerns that traders from different banks worked together to influence currency prices.
The probes come after a number of banks, including RBS, have been handed large fines for rigging of interest rate benchmarks such as the London Interbank Offered Rate.
"Evidence exists that these banks colluded to manipulate exchange rates in foreign currency trades," WEKO said. WEKO director Rafael Corazza said WEKO was in touch with some international authorities but had not been prompted by a foreign authority to open the investigation.
The move comes as reports suggest that RBS is preparing to hire Ewen Stevenson from Credit Suisse as its finance director.
Mr Stevenson, co-head of Credit Suisse's investment bank in Europe, the Middle East and Africa, worked on the £45 billion taxpayer bail-out of RBS in 2008.
Nathan Bostock, who has occupied the job since October, is leaving for Santander UK.