Not that it's entirely authoritative, but I found this info.
From: http://www.creditinfocenter.com/cards/crcd_buy.shtml#Question9Can mail-order merchants charge my card before they ship?According to Janet Hug of Visa USA, "a merchant is not permitted to bill ahead of time" except in case of a deposit or down payment that the customer agrees to.
MasterCard said in a letter that a merchant can charge you before shipment only if s/he tells you and you agree to "the terms and conditions of the sale."
American Express said the merchant can charge your card as soon as you give your account number; but if you receive the bill before the merchandise, call Amex customer service and you don't have to pay while they investigate.