New York's financial regulator has sent subpoenas to Goldman Sachs, Credit Suisse, BNP Paribas and Societe General, expanding its probe into the possible rigging of foreign exchange rates through computer programmes, people familiar with the matter said.

The state's Department of Financial Services, overseen by superintendent Benjamin Lawsky, is looking at whether computer programmes allow banks to front-run or otherwise take advantage of clients, the sources said.

The department is already probing Barclays and Deutsche Bank over their electronic trading platforms and installed monitors in those banks for a closer inside look at what's going on.

A monitor was installed at Deutsche Bank last month, Reuters reported, and at Barclays in November.

The subpoenas to the four banks went out in December, according to one person familiar with the matter. They ask for information relating to the discretionary actions by the banks in implementing algorithms to accept or reject trades.

The banks are in the process of producing the information demanded, another source said, and have met with state officials handling the investigation.

At issue is a latency period between the time an offer is floated and accepted. At least one bank claims the pause is to protect it from high-frequency traders.

The probe may raise the stakes for banks, suggesting that the price manipulation may extend beyond the alleged collusion to a possibly more systemic form of manipulation.

Representatives at Goldman Sachs, Credit Suisse, BNP Paribas, Societe General and Lawsky's office were not immediately available for comment outside regular business hours.

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