Is an unjust law invalid only because it does not conform to the moral values or do other factors also play a role in deciding if a law is proper or not? Lex iniusta non est lex, simply translated, “an unjust law is not law”, has come to be known as one of the bedrock principles propounded by natural law theorists. More specifically the phrase has been attributed to the medieval natural law theorists. Its origins can be narrowed down to the directives of St. Augustine and the principle was thence made popular by Thomas Aquinas. This principal till date, is ascribed to be the starkest difference between natural law and positive law. While natural law theorists set out that determining whether a law is valid or not involves engaging in moral reasoning that ascertains if a law is just or unjust, positive law theorists advance that a law’s validity is a social question that is distinct from the merits of the law.1 The title question demands an exploration through the various factors that render a law invalid. In this paper, by majorly using the directives put forward by Aquinas and that of Augustine, I will attempt to explain what factors constitute to make a law unjust and the authority these unjust laws hold. By doing this I hope to argue that the authority of every positive law is to an extent limited by morals.