Stores are violating their contract with the credit card companies if they set minimum or maximum charges, or force you to show ID in addition to your credit card (with the obvious exception being for age-limited purchases). Depending on your state and your card issuer, surcharges or “convenience fees” may be banned as well. The best way to straighten these guys out is to report them to the credit card company. People who have done so on the Credit Boards message board say that when they report a merchant, they get a letter from the credit card company and when they go back to the store, the shenanigans have stopped. Here’s all the contact infos for the credit card companies to file a merchant complaint, as well as links to merchant agreements, in case you feel like standing up for your consumer rights. Someone better warn Amy’s Ice Cream!

Visa
Phone Number: 1-800-VISA-911 (International: 1-410-581-9994). Or call the number on the back of your card
Mailing Address:
Visa U.S.A. Inc.
P.O. Box 194607
San Francisco, California 94119-4607
Online: Your card issuer’s website may let you send them complaints about merchant violations and start a dispute if your were charged a fee to use your card.

“Visa merchants are not permitted to establish minimum transaction amounts, even on sale items. They also are not permitted to charge you a fee when you want to use your Visa card.”

“Although Visa rules do not preclude merchants from asking for cardholder ID, merchants cannot make an ID a condition of acceptance. Therefore, merchants cannot refuse to complete a transaction because a cardholder refuses to provide ID. Visa believes merchants should not ask for ID as part of their regular card acceptance procedures.”

See this VISA faq on how minimum charges are not allowed.
Rules for Visa Merchants.

MasterCard
Make a report online.
Phone Number: 1-800-MASTERCARD (International: 1-636-722-7111) Or can also call the number on the back of your card.

“A merchant must not require, or post signs indicating that it requires, a minimum or maximum transaction ammount to accept a valid MasterCard card.”

“A merchant must not refuse to complete a MasterCard card transaction solely because a cardholder who has complied with the conditions for presentment of a card at the POI refuses to provide additional identification information.”

MasterCard Merchant Rules

American Express
Make a report online
Phone Number: 1-800-528-4800 (International: 1-336-393-1111)
Mailing Address:
American Express
P.O. Box 297812
Ft. Lauderdale, FL 33329-7812

“American Express’s regulations do not explicitly prohibit minimum charges, but its policy is to discourage any merchant practices that create a “barrier to acceptance.” Amex does prohibit “discrimination” against the Amex card, however, so if a merchant has no minimum or maximum charge or require ID for Visa and MasterCard, the merchant may not discriminate against Amex by imposing a minimum or maximum charge or requiring ID.” [gofso]

RELATED:
MEGA UPDATE: Requiring Minimum Credit Card Purchases is a Violation
Stores can’t set credit card minimum [MSNBC]
California Civil Code Prohibiting Surcharges for Credit Card Use
What Merchants Can And Can’t Do In Regards To Credit Cards
Google Answers on State Laws Regarding Surcharges

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