The European Union's top court ruled Thursday that U.S. credit card giant MasterCard was at fault over its fees on cross-border transactions, which it said restricted competition. Upholding a 2007 finding that MasterCard had appealed, the European Court of Justice said the company's use of interchange fees had forced merchants to raise prices on the customers. When a customer uses a credit card, the merchant's bank has to pay a fee to the buyer's bank for the service.In turn, the bank charges the merchant a fee to cover this cost, which is then added to the price of goods on sale, affecting all customers including those who do not pay by credit card.The European Commission, the EU's executive arm, argued this system and the variety of fees involved hindered "development of an internal market in card payments and related markets, such as internet and mobile payments."