“How do you know this is a surprise tacked on at the end? How do you know there isn’t a mention of the surcharge prior to ordering?”
If it was explained up front, no problem. One can get up and walk out without ordering.
What exactly would you do if they did not do that and simply tacked it on at end without telling you upfront?
I wouldn’t pay it and I’m sure they would have a very difficult time collecting it from their customers. You think the police would arrest you for walking out without paying the surcharge? No legal basis for doing so. Otherwise, any business could add all sorts of surcharges after the fact.