That's about checkout fees, not minimum charge amounts. Minimum charge amounts used to be forbidden by basically every merchant agreement, but thanks to Dodd-Frank and a lot of retailer lobbying, such contact terms are now illegal. Card issuers must allow a restriction on charge amounts (no more than $10 IIRC) if the retailer so desires.

You're right. I meant to include Visa's complaint form, https://usa.visa.com/checkoutfees/contact.jsp which mentions the right for US retailers to set minimums up to $10.

It is worth noting minimums can not be set for debit card transactions.

Lots of small vendors have a minimum anyway, and Visa does nothing about it as far as I can see.

Here in Sweden you're not allowed to charge any sort of additional surcharge, but you are allowed to simply refuse accepting payment with Visa/Mastercard for purchases under a certain amount.

I wonder whose lobbying dollars we have to thank for this law.