A local café has introduced a minimum spend of £15 for card transactions, blaming the processing fees. I haven't eaten there since, on my own I just don't spend enough to go to more than half of the minimum spend.
The newsagent on the platform at Ely (to keep it somewhat railway-related!) put a sign up in March saying 'after 20-something years' it will no longer accept cards for just buying a newspaper - so cash only! - due to the increased card processing fees.
I take the point made by those above that if only a tiny minority are paying cash then that effectively causes a maximum in costs for the retailer. But I'd argue in many cases that's their own fault for incentivising paying by card/contactless/app over the last N years - if the majority of people still paid in cash, they wouldn't have that problem. You don't need to put the conspiracy hat on to see that if you create a duopoly that everyone is dependent upon, that duopoly is going to try to take advantage of the situation - and it appears they have by massively increasing their fees. If there are no alternatives - at least not until something like Bitcoin is more widely accepted, if it ever is - then they're now stuck, in a way they never were with widespread acceptance of cash.