Why would it be illegal to charge you a percentage for using a d

Villas - Why would it be illegal to charge you a percentage for using a debit card. Do they ever ask if it’s a credit card or debit when you use it? No! It’s still a card, not cash! If it’s such a problem use cash, I really don’t understand why this is such a problem, you know what’s going to happen, be kind move on.