Is it legal for an employer to prohibit employees from drinking alcohol and using tobacco 24 hrs prior to work?

Under Georgia law, an employer has the right to choose the employees it wants and to not choose persons he does not want to work for him. His reasons for rejecting an employee are irrelevant except when they violate federal discrimination laws. There is nothing in federal discrimination laws that prohibits an employer from refusing to hire, or from deciding to fire an indvidual who drinks or smokes. There is nothing that requires you to go to work for that person, or to remain that person's employee. This is the meaning of employment at will, which is an important feature of Georgia's common law of employment. Another way of putting this is to say that it is governed by the Golden Rule. He who has the gold, makes the rule.