It is a well-known historical fact that both Martin Luther and John Calvin believed in natural law... "there is no real discontinuity between the teaching of the reformers and that of their predecessors with respect to natural law. Not one of the leaders of the Reformation assails the principle."
... The pressure to abandon the teaching of natural law does not arise from faithful biblical interpretation or from arguments internal to the logic of christian theology; rather it derives from developments in modern philosophy, especially utilitarianism and positivism. Combined with the loss of confidence in the truthfulness of Scripture and the competence of the church to interpret it aright, there arose a widespread skepticism about the ability of reason to discern a universal moral order in human society. That prepared the way for the administration of law to become subject to those who hold the instruments of power. The slogan "might makes right" expressed the prevailing sentiment within the totalitarian states ruled by Fascist and Communist ideologies. The totalitarian states under Hitler and Stalin manipulated laws to promote the self-interests of dictators who held a monopoly of power and disregarded the welfare of citizens. For the most part, the churches were powerless to mount any effective resistance; a measure of their impotence can be traced to their own lack of support for the validity of a universal natural moral order as the highest court of appeal.
(A Lutheran Affirmation of the Natural Law. Carl Braaten. in Natural Law. A Lutheran Reappraisal. pp. 6,7.)
Utilitarianism is the theory of morality that asserts that what determines right from wrong conduct is the degree of its usefulness in providing pleasure and happiness.
Positivism is a theory of knowledge that holds that all real knowledge must be based on sense perceptions subject to empirical verification.