A widening probe of the foreign-exchange market is roiling an industry already under pressure to reduce costs as computer platforms displace human traders.

Electronic dealing, which accounted for 66 percent of all currency transactions in 2013 and 20 percent in 2001, will increase to 76 percent within five years, according to Aite Group LLC, a Boston-based consulting firm that reviewed Bank for International Settlements data.

The push toward electronic trading probably will lower costs for customers and boost transparency of pricing, according to Cormac Leech, an analyst at Liberum Capital Ltd. in London. It may also squeeze margins for banks, he said.

Deutsche Bank AG, Citigroup Inc., Barclays Plc. and UBS AG are the four biggest currency-trading banks, according to a May survey by Euromoney.

Banks including UBS, Goldman Sachs Group Inc. and Citigroup have banned dealers from using multiparty chat rooms.

Banks' income from foreign exchange already has been squeezed.

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