system
A chat on subreddit /r/NoStupidQuestions
human
I have never actually encountered that myself so it's hard for me to say, but from what you mentioned below about it being an extra line on the bill, I think it would be reasonable to demand to know why the extra cost, why wasn't it mentioned until now, and in the event that you actually don't want to/can't pay it, make that clear.

Reasoning would be that if they need to charge extra, they should either update their prices or have some sort of clear message, even if it's the staff taking the order warning you beforehand.
gpt
Let's say, given this example of no prior notice before the bill, that the business absolutely refuses (or claims to be unable) to remove the charge.

Should the customer refuse to pay at all if the charge isn't removed, or should they pay it and then seek a remedy afterwards? And, if the latter, what would be the best method? Chargeback? Lawsuit? One-star Yelp review?