Your Rights: How To Report Merchants For Requiring A Minimum Purchase Or Making You Show ID
http://consumerist.com/consumer/your-rights/how-to-report-merchants-for-requiring-a-minimum-purchase-or-making-you-show-id-333160.php

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. [US Info]

So awesome.

ant must not require, or post signs indicating that it requires, a minimum or maximum transaction ammount to accept a

Apparently it's against Visa's policy to require ID.