American Express Co. defended its prices for currency conversions after a report said employees boosted rates for some business customers without notifying them.“We have training, control, and compliance oversight and believe that our transactions are completed and reported in a fair and transparent manner at the rates which the client has authorized,” Marina Norville, a spokeswoman for the company, said in an emailed statement.Shares of American Express dropped Monday after the Wall Street Journal said the practice had been going on for more than a decade and affected mostly small and midsize businesses. The FX International Payments business accounts for less than half of one percentage point of overall revenue, Norville said in the statement.American Express fell 1 percent to 102.85 in early New York trading at 8:04 a.m.Current and former employees told the newspaper that AmEx's commissions-driven culture encouraged the practice. Customers were recruited with low initial rates, but weren't informed that those prices were subject to change without notice, according to the Journal.The company began to scale back on the practice after media reports of a similar strategy at Wells Fargo & Co., according to the newspaper.

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