(a) Except as provided in subsections (b) through (d) of this Code section, no department of the state government or any political subdivision thereof shall employ any alien for any purpose until a thorough investigation has been made and it is ascertained that there is no qualified American citizen available to perform the duty desired.

(b) An institution of the University System of Georgia may employ an alien who is attending such institution as a student. Such an institution may employ any other alien for a period of time not to exceed one year or may enter into exchange professorship agreements with institutions, foreign or otherwise, where aliens are involved for a period of time not to exceed one year.

(c) The prohibition of subsection (a) of this Code section shall not apply to the employment of an alien who is not a Communist and who is in this country as a student enrolled in a college or university in this state or in a program of student exchange sponsored or participated in by a college or university in this state, as certified by the dean or registrar thereof.

(d) The prohibitions of subsection (a) of this Code section shall not apply to the employment of aliens licensed under Code Section 43-34-33, relating to the licensing of aliens to practice medicine or pharmacy.