A Commerce Commission probe into the foreign exchange market was sparked by a whistleblower, the regulator said.
The commission is investigating possible manipulation of currency rates and benchmarks in foreign exchange markets, and said in a statement today it "was commenced as a result of a leniency application under the commission's cartel leniency policy."
The regulator can offer immunity from prosecution to the first member of a cartel who comes clean and provides evidence, as a means to stamp out anti-competitive conduct.
Policymakers have been sitting on legislation to criminalise cartel conduct since it was first introduced to Parliament in 2011. Commerce Minister Craig Foss introduced a supplementary order paper tweaking the legislation in December.
The New Zealand regulator's investigation into currency trading comes as at least a dozen authorities in North America, Asia and Europe conduct inquiries into claims traders colluded with their counterparts at rival banks to set foreign exchange rates by sharing client information.