In 1996, Visa/MasterCard headquarters introduced a new regulation requiring all businesses who manually key in the majority of their credit card transactions to have a special fraud prevention feature on their credit card processing equipment. This feature is referred to as an address verification system (it checks to see that the billing address given by the customer matches the credit card). If you opt not to use AVS, VISA and MasterCard will not support your transactions and will charge you an additional 1.25% on those sales.