(a) As used in this Code section, the term "extortion" means an unlawful taking by a public officer, under color of his office, from any person of any money or thing of value that is not due to him or more than is due to him.

(b) Any public officer who shall by himself, his deputy, his agent, or other person employed by him be guilty of extortion in demanding or receiving other and greater fees than by law are allowed him shall be guilty of a misdemeanor and shall be dismissed from office.