Merchants are calling on the Reserve Bank to investigate allegations that CBA and other banks have inflated the cost of accepting card payments since the beginning of September.Bank statements seen by Banking Day show that CBA amended acceptance fees it charges for electronic card payments on 1 September 2017.Merchants claim they were not given any notice of the changes until they received their invoices from the bank in early October.One NSW retailer who was previously on a "Bundled Plan" offer was horrified to learn his fees had risen by more than 61 per cent on his September invoice.The fee hikes came after CBA switched thousands of merchants onto new "Interchange Plus" plans.The NSW retailer incurred A$693 in acceptance fees on recorded transactions of $111, 251 in August. That equated to a total fee rate of 0.62 per cent.However, in September CBA assessed the merchant's fees at $1088 on recorded transactions of only $108, 573. The fee hike means the bank is now claiming one per cent of the merchant's sales that are settled with cards.Merchant contracts are subject to contract law and require period of notice and notification of changes in terms - so it will be up to CBA to prove it adhered to its own merchant contract when it moved business customers on to Interchange Plus plans.Banking Day has been told that the negative impact of plan switching on CBA business customers is a matter that will be referred to the Reserve Bank by several industry groups, including the Australian Retailers Association.ARA chief executive Russell Zimmerman said the rising acceptance costs triggered by the banks and the card schemes had imposed pressures on merchants to recoup costs."Most retailers would prefer not to surcharge but if merchants keep getting hit like this they will have to look at cutting costs either by changing banks or finding savings in their supply chain expenses," he said.Card schemes are also boosting fee rates on high volume businesses, which have traditionally enjoyed discounts on merchant and scheme fees.Rob Anderson, the owner of APCO Petroleum - a retail petrol chain in regional Victoria - told Banking Day his Mastercard scheme fees had doubled from 7.7 cents per contactless transaction to 15.4 cents since the start of July."About five years ago our costs on debit transactions were zero and now they seem to escalate every year," he said."What stinks most of all is that Coles and Woolworths and other big petrol retailers are paying much lower fees, so the banks and the regulators are delivering them a cost advantage over smaller businesses like ourselves."Anderson declined to identify his bank, but said it was not CBA.The controversy over the latest fee hikes at CBA and the card schemes come at a sensitive moment for the banking sector, with the RBA signalling on Friday it will mandate debit card reforms if the banks are unwilling to remove anti-competitive practices.At the top of the RBA's reform agenda is its push to get the banks to allow merchants to route