If the hotel is clear about these terms, then I don't see much of a problem with this. It makes it really easy to know to pick a different hotel.
Just because something is written into the terms of an agreement doesn't make it legal.
But it depends why you're being slapped! Obviously we can't go prosecuting everyone who intentionally whacks into someone else according to the rules of whatever sport they're playing, so we make an exception for that. This gets tricky with sports like boxing where the rules require you to do something that looks pretty much like a brutal assault, so the exceptions in that case get pretty finicky -- we might insist that you make your mutual-battery deals in public, in licensed boxing rings, instead of by giving Brad Pitt a nice manly handshake in the basement of a bar and refusing to talk about it later.
And then there's the whole gray area of less socially-accepted sports, like Quidditch or BDSM. We (even prosecutors) often approach things from the perspective of, "if this activity seems normal to me, it must be legal; if it seems wrong it must be illegal." When moral judgments and fear of the unknown creep into that analysis, it can lead to some twisted logic to justify the outcome we know must be right.
[1] Now consider whether you can be prosecuted for A&B as an accomplice.
Your contract would be unenforceable btw - I could slap you three times (hell make it twenty) and walk off - you could not get any court to enforce payment. You could threaten to accuse me of assault if I did not pay up - but then you are blackmailing me and would do more time than I would for assault.
But I suspect that the hotel owner has been slapped by a couple of brides over this :-)
A legal contract depends on mutual understanding. People learning to box generally understand they are going to get hit. People booking a wedding party generally don't expect to be held responsible for their guests having opinions they post online. The hotel would have to make this policy very clear in order to achieve mutual understanding, and that doesn't mean just putting it on the contract and the webpage for the customer to find on their own.
Participation in a contract that specifically covers terms for being slapped also bring with it an expectation of being slapped.
It's not enough to have language in a contract. There needs to be understanding by both sides about what is being agreed to.
Since the Internet engaged mob-mode before engaging investigation-mode, we don't know how clear these terms are to people who are booking weddings.
It might be very clear because they send an email explicitly telling the bridal party about these terms and asking them to consent, which would also be a signal to the party about the quality of online reviews. Or it might be buried in the middle of 12 other clauses and the customer doesn't know about it.
Similar pieces of other contracts are valid and common and are called "non-disparagement clauses". I don't see how this differs.
I'm not sure that I believe this. I can believe that there are some places out there that think that they can get away with enjoining you against posting negative reviews (until the law eventually settles down against that, as I'm sure that it will), but I find it hard to believe that there are many places that think that they can fine you for the actions of other people. Can you give examples?
EDIT: As baddox (https://news.ycombinator.com/item?id=8131575) politely points out, I worded this badly. I want to say something like "the actions of other people over which you have no reasonable expectation of control" (for example: you can reasonably be expected to prevent guests in your room from damaging the furniture, but you cannot reasonably be expected to monitor the Internet usage of all your guests after they leave to make sure that they do not post a negative review).
I'm not a lawyer so maybe I'm missing something obvious. I would just like some substantiation. It seems that many people have the habit of automatically declaring something they don't like to "must be illegal" simply because they strongly dislike it. That's now how law works, and that's important to understand because many people seriously underestimate the powers that the legislature holds.
I didn't claim that it was (il)legal or (un)reasonable, only that I wasn't convinced that language of this sort (where you are being held responsible for the actions of people when they are not under your immediate control) was common in contracts.
There are plenty of examples of that, even in the context of hotel booking. The person who pays for a hotel will be fined if non-paying guest damage hotel furniture, for example.
When you attend a wedding, you have absolutely no say in the venue. Yes, the bride and groom may have agreed to the terms, but the attendees did not have a choice.
So if they get shitty service and want to post a review about it online, they find out doing so will cost the bride and groom $500. It might not be clear cut extortion - but it is not an acceptable business practice.
Just because I sign a contract saying I agree to pay $1 everytime someone I know says something unkind to anyone doesn't mean the contract is enforceable.
Besides I don't think the he meant extortion in the legal sense but more the moral sense.