No person, firm, corporation, unincorporated association, State agency, unit of local government or any public or private entity shall deny or refuse employment to any person or discharge any person? from employment on account of the fact such person possesses sickle cell trait or hemoglobin C trait. The term “sickle cell trait” is defined as the condition wherein the major natural hemoglobin components present in the blood of the individual are hemoglobin A (normal) and hemoglobin S (sickle hemoglobin) as defined by standard chemical and physical analytic techniques, including electrophoresis; and the proportion of hemoglobin A is greater than the proportion of hemoglobin S or one natural parent of the individual is shown to have only normal hemoglobin components (hemoglobin A, hemoglobin A2, hemoglobin F) in the normal proportions by standard chemical and physical analytic tests. The term “hemoglobin C trait” is defined as the condition wherein the major natural hemoglobin components present in the blood of the individual are hemoglobin A (normal) and hemoglobin C as defined by standard chemical and physical analytic techniques, including electrophoresis; and the proportion of hemoglobin A is greater than the proportion of hemoglobin C or one natural parent of the individual is shown to have only normal hemoglobin components (hemoglobin A, hemoglobin A2, hemoglobin F) in the normal proportions by standard chemical and physical analytic tests, provided, however, that this section shall not be construed to give employment, promotion, or layoff preference to persons who possess the above traits, or to prevent such persons being discharged for cause. (1975, c. 463, s. 1.)