(Adds details about the probe)
BRASILIA, Sept 18 (Reuters) - Brazilian antitrust watchdog CADE opened an investigation into the country's largest banks on Tuesday for allegedly using their market position to corner the cryptocurrency trade to the disadvantage of brokers.
CADE said it was looking into alleged monopolistic practices by Banco do Brasil SA, Banco Bradesco SA, Itau Unibanco Holding SA, Banco Santander Brasil SA , unlisted Banco Inter and cooperative bank Sicredi.
The investigation was requested in June by the Brazilian Association for Cryptocurrency and Blockchain (ABCB), which said the banks were abusing their power as financial players by closing accounts of brokerages trading in bitcoins.
CADE said in a report calling for the investigation that information it collected indicated that "in fact, the main banks are imposing restrictions or even prohibiting ... access to the financial system by cryptocurrency brokerages."
The banks argued, in response to questions from CADE, that the accounts were closed because of the absence or lack of client data that is required by law to prevent money laundering.
Brazilians investors have taken enthusiastically to trading in bitcoins and now have more cryptocurrency accounts than stock brokerage accounts, which has put regulators on the defensive.
Brazil's Securities and Exchange Commission, CVM, banned investment funds from trading in cryptocurrencies earlier this year, although it later said indirect ownership was allowed. (Reporting by Iuri Dantas; Writing by Anthony Boadle; Editing by Christian Plumb and Peter Cooney)