Nope, there are no laws prohibiting this. If an employer wants to have "cocktail hour" 24/7 on their premesis, they are free to do so no matter how bad an idea it is. It's certainly possible an employer could have civil liability if a drunken employee gets killed or kills someone while driving home however.
The great majority of employers prohibit alcohol in the workplace and have work rules prohibiting employees from reporting to work while under the influence. With the exception of certain professions (pilots, truck drivers, train conductors, etc.) that are regulated due to public safety issues, these are voluntary policies and work rules.
