In a ruling issued last week, NMA accuses Interpay of abusing its dominant position on the market for network services for PIN-based debit-card transactions by charging excessive rates. The decision followed a year-long probe into the structure of the domestic payment market.

The watchdog has also penalised the eight banks which established Interpay, with individual fines ranging from EUR3.9 million for the top three banks to EUR0.5 million for the bottom three. In its ruling NMA said the eight banks had effectively ruled out competition by deferring to Interpay.

In a strongly-worded response, Interpay has said it will appeal the ruling, which it argues contains "serious errors". Interpay accuses the watchdog of asking retailers leading questions designed to induce a negative response.

In a statement, Interpay says: "The study is not objective; moreover it is not representative. Interpay cannot help but believe that the NMa purposely worked toward the outcome and conclusion of the study."

The payments body says the higher fees charged in the early days of the debit card network reflected the costs and risks involved in establishing the infrastructure. Since then, it points out, the rates for PIN-based payments has halved.

"A company that abuses a position of power, however, would never halve its rates," states Interpay.

A study performed by De Nederlandsche Bank also indicated that the PIN rates applied in the Netherlands are among the lowest in Europe. In Germany, France and Italy, for example, shop owners pay no less than six times the rate applied in the Netherlands for PIN transactions, says Interpay

In response, the competition body says that returns generated by Interpay from PIN-based debit processing are "five to seven" times higher than those that would apply under NMA benchmarks.