I am sorry, but this guy is way out of line here. Legally I have no idea, but morally, I do. I mean, go to the place and talk to someone. Or take down the site. Don't start a campaign for your feelings. edit: On second thought I was eating a restaurant when their televisions turned black and the screen came up with a pay your bill now notice. Every screen in the restaurant. So I guess maybe this is the tactic.
In my opinion, the only reason this tactic is not recommendable is that it's not deemed acceptable practice from a professional standpoint, and I believe that this is mostly a cultural thing. Everybody says it's wrong, so it must be wrong.
Think about it, if tomorrow all service providers developed a mindset where this kind of shaming in an attempt to collect from deadbeat clients became standard practice, nobody would be advising against it anymore. This is consistent with a lot of everyday nonsense that pass for acceptable, just because that's just the way things have always gone.
I'm not convinced that there aren't places in the world where this is seen as perfectly ok and maybe even expected.