Which type of workplace discrimination occurs when an organization uses an employment practice that results in unfavorable outcomes to a protected class? for example, by requiring that all employees have a high school diploma, the mathis construction company essentially discriminates against those who did not graduate from high school?

This is the adverse impact principle. This action takes place when a company, knowingly or not, takes an action that will effect a person's employment opportunity due to some factor beyond the person's control. When the class a person belongs to is shown to have been a historically disadvantaged class, this can lead to calls for remedy of some form, be it through litigation or mediation of some fashion.