BRUSSELS (Reuters) - EU antitrust regulators are investigating whether the fees charged by Visa and Mastercard ( MA ) have a negative impact on retailers, an EU document seen by Reuters showed.

The European Commission, which enforces EU competition rules, sent questionnaires about both Visa and Mastercard ( MA ) to retailers and payment service providers in September, giving them until October to respond.

Visa and Mastercard ( MA ) have long dominated the market for payment cards, prompting complaints from retailers about so-called scheme fees levied by the two firms in recent years, as well as what they say is a lack of transparency on them.

Scheme fees are charged by a card payment system operator for services relating to participation in the card system.

"We have no further comment to make, as the investigation is ongoing," the EU antitrust watchdog said when asked by Reuters to comment on the contents of the document.

Such questionnaires usually help EU regulators to develop an anti-trust case, which if pursued and successful can lead to fines of as much as 10% of a company's global turnover.

Among the questions asked is whether the number of fees in the EEA, the 27 EU countries plus Iceland, Liechtenstein and Norway, in which the retailer is active and "the continuous introduction of new fees and deletion of existing fees" negatively affected their business in the period 2016-2023.

The questionnaire also asks whether retailers and payment service providers are consulted on the introduction and deletion of fees and fee hikes.

A Visa spokesperson said the company received a request for information from the Commission in late August and was working through it "to supply the relevant information".

Mastercard ( MA ) said: "Governments and regulators around the world want to ensure they have line of sight into how industries work. That's what this is, a simple request for information."

Retailers and payment service providers were asked whether they can negotiate scheme fees, processing fees and innovation fees with Visa and Mastercard ( MA ), and if such discussions are conditioned by the acceptance of specific products from them.

Processing fees are charged by processing entities including card payment system operators to payment service providers for services relating to technical processing for authorising, clearing and settling card payments.

The EU regulators also want to know if retailers and payment services providers are told about the level of behavioural or compliance fees or fines levied by Visa and Mastercard ( MA ) and the justification given for them.

EuroCommerce, whose members include Amazon, Carrefour, H&M, IKEA, Metro and REWE Group, said scheme fee increases and new scheme fees have all but eaten up the reduction of card fees following the 2015 Interchange Fee Regulation.

"We estimated in 2022 this was costing the EU economy some 1.5 billion euros yearly," the lobbying group said.

"With over 800 different scheme fees, we see that acquirers have a hard time implementing them correctly, let alone merchants who often don't understand their value or the cost basis that the schemes claim," it added.

Britain's Payment Systems Regulator flagged similar concerns on such fees in May, saying there is little evidence that big fee hikes have led to a major improvement in service.