BRUSSELS (Reuters) -Europe's largest retailers and online retail giants have urged the European Commission to rein in allegedly high fees charged by Visa and Mastercard ( MA ), saying they hurt the bloc's competitiveness and hamper rivals.

Visa and Mastercard ( MA ) dominate the market for payment cards and have in recent years faced complaints from retailers about their scheme fees, and what retailers say is a lack of transparency on these fees. The two U.S. companies process about two-thirds of card payments in the euro zone.

The retailers' grievances have in part prompted the 27-country European Union to look into alternatives such as a digital euro to lessen dependence on American payment providers. The slow legislative process on a digital currency, however, has frustrated some policymakers and businesses.

"International Card Schemes (ICS) have been able to increase their fees without competitive challenge or regulatory scrutiny. They have also rendered their system of fees and rules so complex and opaque that players are unable to understand, let alone challenge, what they are paying for and why," the retailers said in a letter dated May 13 and seen by Reuters.

The group cited a 2024 report by The Brattle Group that showed a cumulative increase in ICS' fees of 33.9% between 2018 and 2022 - averaging 7.6% per year - on top of inflation, but did not find any corresponding improvement in service for EU merchants and consumers.

Visa and Mastercard ( MA ) did not have any immediate comment.

The letter was addressed to the Commission's antitrust chief Teresa Ribera, financial services commissioner Maria Luís Albuquerque and economy chief Valdis Dombrovskis.

Signatories were EuroCommerce, Ecommerce Europe, Independent Retail Europe, the European Association of Corporate Treasurers and the European Digital Payments Industry Alliance.

Members of the lobby groups include Aldi, Amazon, Carrefour, eBay, H&M, Ikea, Intersport, Marks & Spencer, Worldline, Nexi and Teya.

The letter called on the Commission to take action against Visa and Mastercard ( MA ) under EU antitrust rules, modify the rules on interchange fees by imposing price controls on scheme fees, levy transparency and non-discriminatory obligations on ICSs and introduce a tool for regulators to scrutinise actions taken by the ICSs.