Walmart and Kroger have had their own disputes with Visa (for one example) and (at least Kroger) started blocking some of their cards at select chains in order to negotiate a better deal. Costco has super tight margins. The the point that when their execs are talking about the price of goods they don't say, "[Item] is $70." No, they say, "[Item] is 69.99." Their culture is about every last penny of the margin. Their money comes from memberships.