Merchants say higher fees are forcing them to hike prices. Congress may take up the issue. WASHINGTON — Credit card companies have always taken their cut when a customer uses plastic, part of the cost of doing business electronically. But a surge in the fees has sparked an intense dispute, with small merchants complaining that the higher charges are forcing them to raise prices and, in some cases, threatening to drive them out of business. With the two sides at loggerheads, Congress is preparing to step in on behalf of merchants and consumers.