"547. The relation of civil law to natural law is as follows:
(a) The State has no power to make laws that are opposed to nature,
for, since law is an ordinance according to reason, any human command
that is contrary to nature and therefore to reason is not law, but the
corruption of law. No sin, not even a venial sin, can be made
obligatory by law."
Source: "Moral Theology: A Complete Course Based on St. Thomas Aquinas and the Best Modern Authorities", by S.T.M. Very Rev. Charles J. Callan, O.P. and S.T.M. Very Rev. John A. McHugh, Imprimatur May 24, 1958 A.D.