The European Commission is probing the inter-exchange fees charged by MasterCard for cross-border card transfers.
In a daily press briefing, Commission spokesman Tilman Lueder said the EU executive had sent MasterCard a statement of objections detailing its concerns that the fees charged are too high and lack transparency.
"We are concerned that the so-called inter-exchange fees between the merchant's bank and the cardholder's bank are not transparent, are extremely high," said Lueder.
He said the Commission was not prejudicing the outcome of the investigation and did not rule out the possibility of an amicable settlement. A similar wrangle with Visa in 2001 was brought to a close when the card company agreed to scale back interchange fees and prevent retailers from surcharging cardholders.