well, how about that

[lauralh]

from the Visa Corporate FAQ

Can merchants set a minimum purchase or charge a fee for using my Visa card?
Visa has certain regulations that all merchants that accept Visa cards must follow. One of those rules is that Visa merchants are not permitted to establish minimum transaction amounts, even on sale items.

If you run into a problem like this with a merchant, please notify your Visa card-issuing bank. Visa member banks have access to the appropriate Visa rules and regulations as well as to the Notification of Customer Complaint forms which should be used by the bank to document and file merchant complaints.