Why would one restaurant want to ban smoking in another restaurant? If a group of restaurant owners got together to get the state to ban smoking, isn't that equiviant to price fixing? Why doesn't this group of restaurants just ban smoking in their own places? By the way, I am a non-smoker.
So therefore any ongong argument is speculative (although I don't see associations being particularly anxious to take up the issue).
To answer your question, the only reason price fixing is illegal is because it was made illegal by passing a law. This is the same process that is being used to ban smoking in restaurants. In the event associations wanted to pursue such laws I see no reason why they shouldn't be allowed to. In fact a wide enough ban on smoking would raise income for larger restaurants who would have reduced staffing costs and equipment costs.