A major evidence of this is how the laws are divided. A people group with a certain skin color have laws that differ from others with certain occupations.
Although following the law is something we are all supposed to do, that doesn't mean we do it, however, if it is a cultural norm for everyone to be treated according to their occupation, gender, and wealth than that in itself is the pure definition of inequality.
Furthermore, it is justified because not only is that the cultural norm but it is also the laws they have to follow as part of their culture.