Legislation promulgated by the government in a political society. In general, it is morally binding in conscience, as the Church's tradition since biblical times testifies. "For the sake of the Lord," Peter told the first-century Christians, "accept the authority of every social institution: the emperor as the supreme authority, and the governors as commissioned by him to punish criminals and praise good citizenship" (I Peter 2:13).
What is less certain is the precise nature of the moral obligation of civil laws and under what conditions they are binding in conscience. They are certainly obligatory insofar as they sanction or determine a higher law, whether natural or revealed, as when they forbid murder and stealing or specify the rights of ownership. They are certainly not obligatory when the laws are unjust, notably when they are contrary to the laws of God and of the Church, when they do not proceed from legitimate authority, when they are not directed to the common welfare, and when they violate distributive justice.
Thus a person is not permitted to obey a law that commands acts against the moral law. Yet if an unjust law does not lead one to commit illicit actions, one in practice obey it or even be obliged to do so for reasons or general welfare beyond the immediate scope of the law. Moreover, once a law has been passed by the civil government, it should be considered just unless the contrary is clear from the nature of the law or from the declaration of ecclesiastical authority.