I have been looking through both federal and state labor laws and I can't find where it states that if you work less than fours hours in a day, your employer has to pay you for a full four hours worth of work. I am 99% positive this law exists but I don't know if it is a federal or state law.

It's a state law and it's only a state law in a very few states. Most states do not have such a law and in those that do, it's not always four hours.

Although I believe that NY does have a law, I don't have a link to it. Mlane? Robb?