I'm a big tipper.
Having been a bartender when younger, and having hung out a good deal with other bartenders and wait staff, I know how important tips are, and how hard even mediocre ones have to work.
And how most people who come into bars and restaurants have no clue what all is involved. And how most "restauranteurs" assign way too many tables to individual waiters/waitresses. Next time you go into a restaurant, look at how many tables your waitress/waiter has to serve: the number should be, at most, 6 four-person tables.
If you think my six-table maximimum (actually, it should be closer to 4) sounds small, imagine yourself being the only server of a dinner party for 24. And not just a Thanksgiving dinner served family style, but one where each of the 24 is giving you individual instructions on every piece of the meal, asking you to refill their water and beer, three are trying to chat you up, realizing the goddamn salad station needs filling again and the dishwasher is falling behind and the goddamn bartender is four orders behind because he's dealing with an obnoxious drinker at the other end of the bar.
Yet virtually every restaurant in my area has its staff assigned to between 8 and 12 tables. Not surprisingly, the general level of service around here pretty much sucks.
I'm also a big tipper because I'm a member of one of the most insensitive and undertipping groups of restaurant patrons -- academics. No one complains more than academics about their pay (and don't get me started on how they invariably support liberal ideas that spend other people's money), and I'm betting no occupational group is worse at tipping.
And so I tend to overtip as a matter of habit. Even if the service is mediocre. It takes major incompetence of the sort that would lead me to seek out a manager to complain before I'll leave the miniscule tip that says "no, I didn't forget. you're so bad, that I'm intentionally leaving you a 1% tip."
So I fully understand the "large table" charge. When I've been with a group and it seems to me that the group has undertipped, I will even go back to the table and put some extra down.
All that said, however, did any restaurant I know try this sort of nonsense, they'd never see me inside their walls again. As others say, no one is entitled to a tip.
And, moreover, it really sounds like the restaurant owner is trying to collect a table charge under the masquerade of a "gratuity" or "service charge." I'd love to know how said restaurant distributes their tips. Don't assume that such a mandatory charge, whatever it might be called, ever finds its way to the person waiting the table in question. Don't assume that any tip added to a charge goes directly to your server.
If you want to charge for a big table, fine. If you want to consider those who walked out without paying it scum and put them on the "banned" list and refuse service, do that, too. If you want to tell your staff that from here on out said twits get put on "worst service imaginable" (trust me, there's a lot worse that having to wait an hour for wings in a busy place), do that.
But sue them for nonpayment of a gratuity? I don't care if they were the the table from hell. You're a moron. And you deserve to lose your business.
And do not be conformed to this world, but be transformed by the renewing of your mind, that you may prove what is that good and acceptable and perfect will of God.
Romans 12:2 (NKJV)