That is exactly the type of agreement that the Durbin amendment prohibits. I don't see any mention of state or local laws prior to now, so that seems like a complete non sequitur to me.
Yes, exactly like I said. It prevents processors from requiring merchants not to have minimum charges. In other words, it prevents processors from making agreements with merchants where "requiring minimum purchases is a violation of the merchant-processor agreement". It doesn't stop someone else from stopping the merchant from having a minimum charge, but it does stop the type of merchant-processor agreement that you described.
The start of the thread was the claim that the Durbin amendment made it illegal for merchants to set CC minimums for consumer purchases. That's the false interpretation.
> the law requires that processors allow merchants to have a minimum purchase requirement of up to $10
The Durbin amendment (see quoted statute in other comment) prevents networks from forcing small merchants to accept small charges, not merchants from imposing minimums on consumers.
State and local laws can still prohibit CC minimums via statute or via licensing.