The Financial Post reports in its Thursday edition that Visa and Mastercard are planning to boost the fees that many retailers pay when accepting customers' credit and debit cards. A Bloomberg dispatch to the Post says that the additional Visa charges are slated to begin in October for on-line transactions, followed in April by new fees for commercial credit, debit and prepaid cards. For Mastercard, a new preauthorization fee for credit-card purchases will start in October. With the increases, merchants could pay more than $500-million (U.S.) in additional fees each year, according to merchant-consulting company CMSPI. So-called interchange fees have become a contentious issue in recent years. Bloomberg notes that while Visa and Mastercard set the rates for those fees, it is the banks that issue the cards that keep most of the fees.