Why would merchants need to sue in order to be allowed to reject credit cards for transactions under a minimum amount? Couldn't they just set that as their store policy, kind of like how some stores have policies about unaccompanied minors and how many bad checks get you banned?

@RobertColumbia Because the card network (e.g. VISA) would have a policy saying they're not allowed to do that, and saying if they violate the policy they will be disconnected from the network. The lawsuit would be to make the network let them do it without being disconnected.

@RobertColumbia the networks have a lot of power over the merchants. This is de-facto a duopoly (VISA+Mastercard hold all the market, AMEX, Diners Club, Discovery, UnionPay, JCB - are all local and globally insignificant even combined together). There were multiple anti-trust lawsuits against both MC and VIsa, both in the US and the EU, due to various unfair policies including demanding the merchant accept their cards for all transactions or refuse accepting competitors' cards.

Worth noting also that it's not uncommon for businesses that deal with low-priced items to have a fee that offsets their loss on low-priced transactions. For example finding at the register: "A $0.50 processing fee will be added to any credit card transaction less than $5". It doesn't really avoid the fee which is what OP asked but technically allows the business to offset the loss which is kinda what looks like it spurred the question.

united-states - Unless the jurisdiction forbids (ex. NYC), no merchant is forced to accept cash either. USD is legal tender to pay TAXES to the goverment. A vendor can decide to sell stuff only for otter skins, for example.

@Mindwin federal reserve notes and US treasury coins are legal tender in the US and are valid for paying any debts or obligations. Merchants can refuse services/sales to cash-only customers, but they cannot refuse cash to pay a bill that settles an existing debt (e.g.: paying the check in the restaurant after eating). It's not relevant to this topic, though since I suggested cash as an alternative, not something forced on the merchant.

@littleadv Plenty of shops in Germany accept girocard but not VISA or Mastercard. Apparently, the fee with girocard is around 7–11 cent + 0.18% of the transaction (plus some fixed monthly fees). Cash payments may cost more. For VISA/Mastercard, the costs are almost 10× higher (1.5% of the transaction). I don't wonder why most shops decline VISA/Mastercard, but I do wonder why the equivalent of girocard is rare in some countries.

@gerrit Germany is pretty unique in that regard, similarly Japan (with it's JCB) and the wallgardened China and Russia also have pretty unique arrangements. I believe Eurocheque was also pretty popular in Germany (is?) whereas credit cards not so much. However, I have not seen anything similar in most other countries. Eurocard was pretty popular in Europe (which made Mastercard so, after the merger), and Visa ate Diners Club for lunch in the US.

@gerrit In the US, it's American Express that's frequently not accepted, as their fees are higher than MC/Visa/Discover. I've also seen many small shops that say credit cards aren't accepted for bills less than (say) $10.

@littleadv Please don't spread that falsehood, especially if it's not relevant to the question. federalreserve.gov/faqs/currency_12772.htm from the horse's mouth...

@Joe that page says exactly the same thing as I, and even quotes the USC to that point. What's the falsehood exactly?

(e.g.: paying the check in the restaurant after eating)

A restaurant is "goods or services" just like anything else, the fact that you pay afterwards isn't relevant. A cursory google search shows this (as does the many, many restaurants that don't accept cash). Some cities have special rules, but it's not federal.

@Joe so, what do you see happening in the scenario I described? Restaurants can refuse to seat you if you're a cash-only client, sure. But once you've consumed the food - they become a creditor. They can't refuse a cash payment if you already owe them, that's a debt you're settling, not a service you're purchasing.

This really seems like a separate question, which was sort of my point - it doesn't belong in the comments here.

@Joe you said I'm spreading falsehood. Do you still hold this opinion? If so - please answer, and provide legal basis.