Retail groups are preparing to bombard the Hayne Royal Commission with evidence of price gouging by banks for processing over-the-counter debit card transactions.Small business groups claim that the acceptance fees of thousands of retailers have trebled in the last five years as banks directed them to route contactless payments through the Visa and Mastercard payments systems.Bank statements shown in confidence to Banking Day show that independent petrol retailers are among the hardest-hit businesses for merchant service costs since the boom in contactless payments took off in 2014.For one petrol seller in regional NSW, the average service fee on all debit card payments has blown out from 6.8 cents per transaction in December 2014 to 18 cents in the corresponding month last year.  That equates to a rise of 164 per cent.The bank statements show the retailer incurred A$240 in service fees on $140,000 of debit card purchases in December 2014. However, fees at this merchant blew out to $532 in December last year even though debit card purchases at his petrol station were $17,000 lower at $123,000.Mark McKenzie, the chief executive of the Australasian Convenience and Petroleum Marketers Association, said his organisation had requested meetings with Reserve Bank officials to highlight the need for reform of the payments market.Payments officials at the RBA are stepping up pressure on banks to allow merchants to choose how contactless payments on debit transactions are processed.Eftpos Australia currently processes debit card payments at around half the cost of the Visa and Mastercard systems, but the major banks don't allow merchants to direct the payments to the cheaper processing platform."The convenience of contactless payments has contributed to a dramatic rise in the number of transactions that are processed using the computer chip on the front of a customer's card - as opposed to the traditional black magnetic strip on the back of most cards," McKenzie said."What few may realise, however, is that the net effect of this technological change has been a two to threefold increase in the cost of debit transactions for many retailers in Australia."McKenzie said he was concerned about the surreptitious methods by which banks have boosted service fees."The most astonishing fact about this increase is that it has been quietly introduced by the major banks in recent years, with most of Australia's retail businesses - and their customers - being unaware of the increases," he said.ACAPMA is advising its members to review their existing merchant fee arrangements with banks and to encourage customers to use the swipe facility on debit payments.McKenzie said the rise in merchant fees meant that the acceptance costs of some petrol retailers had ballooned by $15,000 a year."The rate at which these fees have risen is unacceptable," he said.ACAPMA is preparing a submission to the Hayne Royal Commission, in which it will provide specific evidence of fee gouging on merchant fees.Other peak industry bodies, including the Australian Retailers Association and COSBOA, are also expected to highlight merchant fees as centrepieces of their submissions.