The probe follows a formal complaint by the German Federal Anti-Trust Office. It wants the EC to take action against FIFA, soccer's global governing body, for stipulating that credit-card payments for World Cup tickets can only be made using a MasterCard.
The complaint is the second of its kind to be lodged with the EC. Which?, the UK consumer group, issued a similar appeal last month, but it was initially dismissed by the Commission, which said it did not believe the arrangement with MasterCard was anti-competitive.
However, the intervention of the German organisation has persuaded the EC to launch an in-depth inquiry.
Sports industry insiders believe that, if the EC rules against FIFA and denies MasterCard payment exclusivity, the credit-card giant will be within its rights to demand compensation, as the contractual clauses of its sponsorship will not have been fulfilled.
The row comes at a crucial time for FIFA, which is in the middle of negotiations with MasterCard over the renewal of its sponsorship. The deal between the two expires after the 2006 World Cup.
FIFA hopes MasterCard will spend up to three times more for its sponsorship than at present. The eight-year deal under discussion is part of the governing body's plan to cut its portfolio of primary commercial partners from 15 to six.
A spokesman for FIFA stated that it had met all contractual obligations and would not comment further until the EC inquiry had been concluded.