National Australia Bank has come under fire from federal small business ombudsman Kate Carnell for its decision to impose a new transaction fee on business customers making real time payments through its banking website.The bank confirmed on Monday that it would introduce a transaction fee of 40 cents each time a business customer executed a NPP-related payment through its NAB Connect service.NAB began notifying business customers in December that the new fee would apply to PayID transactions using the Osko service.While the bank is currently waiving the fee, a spokesperson said it would be levied on business customers using the NAB Connect service from 1 May.Carnell said she was surprised by NAB's decision, given the bank's track record of consulting with business groups.She also noted that the pricing decision was not raised in a briefing the bank gave the Australian Small Business and Family Enterprise Ombudsman in December."From our perspective, the NAB consults with small business groups better than other banks," she said."We met with them in December and fascinatingly they forgot to tell us about this one."Carnell said the new fee was a "stupid" move that defied logic for a bank that specialises in small business banking."It looks like incredibly stupid marketing for a bank that is selling itself as a small business bank and that thinks it understands its customer base," she said.The ombudsman's office wants the bank to reconsider the pricing decision, although Carnell acknowledged that NAB had a right to retrieve costs of providing faster payments from all customers.However, under the pricing arrangements announced by the bank, retail customers have escaped having to pay fees for Osko and other real time transactions that might become available through the NPP."It wouldn't be appropriate for the bank to use this transaction fee as a cash cow or to subsidise consumers through small business customers," she said."Small business is the meat in the sandwich, here."NAB has not explained why it decided to levy the transaction fee on business customers beyond saying that NPP and Osko payments were being treated as a "premium service" on the NAB Connect platform.Banking Day has sought further comment from the bank.