SAO PAULO/BRASILIA (Reuters) - Fifteen of the world’s largest banks are under investigation on suspicion of rigging the Brazilian currency, antitrust watchdog Cade said on Thursday, the first such probe in one of the busiest foreign exchange markets globally.

A man walks past a board showing the Real-U.S. dollar exchange rates in Rio de Janeiro March 4, 2015. REUTERS/Sergio Moraes

In a document, Cade alleged that the banks colluded to influence benchmark currency rates in Brazil by aligning positions and pushing transactions in a way that deterred competitors from the market between 2007 and 2013, at least. Foreign exchange trading in Brazil is estimated at about $3 trillion a year, excluding swaps and derivative transactions.

The banks named in the Cade probe are Bank of America Merrill Lynch BAC.N, Bank of Tokyo-Mitsubishi UFJ [MTFGTY.UL], Barclays Plc BARC.L, Citigroup Inc C.N, Credit Suisse Group AG CSGN.VX, Deutsche Bank AG DBKGn.DE, HSBC Holdings Plc HSBA.L, JPMorgan Chase & Co JPM.N, Morgan Stanley & Co MS.N, Nomura Holdings Inc 8604.T, Royal Bank of Canada RY.TO, Royal Bank of Scotland Group RBS.L, Standard Bank Group Ltd SBKJ.J, Standard Chartered Plc STAN.L and UBS AG UBSN.S.

The Brazilian investigation comes weeks after six of the world’s largest financial institutions agreed to pay $5.8 billion to the U.S. government to settle charges of currency rigging. The U.S. probe took more than five years and five of those banks, which are being probed by Cade, pleaded guilty.

Globally, currency trading is estimated at around $4.7 trillion a day and has been targeted in recent government probes in Europe, the United States and Japan. Those probes allege that banks prioritized the execution of their own currency trades at the expense of client orders, taking advantage of the fact that those deals often take place away from exchanges.

The Cade probe highlights the growing importance of international cooperation in efforts to root out different forms of market rigging. It sets a milestone for a country long characterized for lax law enforcement standards for white-collar crime.

“The probe will probably follow similar patterns to those that took place in larger financial hubs, with banks seeking a settlement with Cade instead of fighting the accusations in courts,” said Luís André de Moura Azevedo, a capital markets law professor with Fundação Getulio Vargas in São Paulo.

There were no signs that Brazilian banks participated in the scheme, Cade superintendent Leonardo Frade said at a news conference in Brasilia. The watchdog has yet to estimate how much money the banks or the individuals cited in the probe made with the scheme, he added.

‘THE MAFIA’

Bank of America, Barclays, Citigroup, Credit Suisse, UBS, Standard Bank, Royal Bank of Canada, Standard Chartered, and Royal Bank of Scotland declined to comment. Nomura, JPMorgan, Deutsche Bank, Standard Bank, Tokyo-Mitsubishi and HSBC did not have an immediate comment.

In the current probe, Cade said traders who described themselves as “The Cartel” or “The Mafia” used online chat rooms to fix their positions ahead of market trades. Another 30 individuals that might have participated in the scheme are also under investigation, the watchdog said.

At least one of the alleged participants is cooperating with the current investigation, Frade said. The person is seeking total immunity from any type of penalty that Cade could impose, such as fines and temporary or permanent bans from the securities industry, Frade noted.

The Cade document said traders probably front-ran client orders and pushed through trades that affected the way benchmarks like Brazil’s PTax and WM/Reuters rates were set. They might have also colluded to fix spreads on client trades, unveil spot and future trades that should have been kept confidential and even deal flow volume data, the document added.

Benchmarks like the PTax or the WM/Reuters are used by investment firms to value their assets on a day-to-day basis.

“We’re trying two different fronts in this investigation: first, about the banks’ trading practices with onshore Brazilian clients and, second, how the banks traded the Brazilian real for other currencies,” Frade said.

The trades were shared and discussed in online chats through Bloomberg terminals, Cade said. Bloomberg LP and Thomson Reuters Corp TRI.TO, the parent company of Reuters News, compete in the financial information market, providing analytical and communication tools for investment professionals.

Both Bloomberg and Thomson Reuters declined to comment on the Cade investigation.

The real BRBY gained 1.6 percent to 3.0991 reais to the dollar on Thursday. Traders said the Cade probe had no impact on currency prices.