An ordinance issued by legitimate authority in the Catholic Church. The legislators for the entire Church are the Roman Pontiff alone, or the Pope through the Roman Curia, or an ecumenical council together with the Pope; the bishops for their individual dioceses, or conferences of bishops for the territories under their jurisdiction; and the major superiors of institutes of perfection for their members, according to the repsective constitutions.
The Catholic Church has always professed her right to pass laws that are binding on the consciences of the faithful. This right is believed to be of divine origin, since "the Church, our most prudent Mother, by the constitution received from her Founder, Christ, was endowed with all the qualities suitable to a perfect society. So, too, from her very beginning, since she was to obey the Lord's command to teach and govern all nations, she has undertaken to regulate and protect by the laws the discipline of clergy and laity alike" (Benedict XV, Providentissima Mater Ecclesia, May 27, 1917).
Every baptized person, even if one is not a professed Catholic, is subject to ecclesiastical laws except in such cases as are indicated in the law. The obligation stems from the fact that by the sacrament of baptism "we are made members of Christ and of his body, the Church" (Council of Florence, Denzinger 1314). Baptism is, in fact, the janua Ecclesiae, the door of the Church. Since the baptismal character is indelible, a person once baptized always remains subject to the Church into which he or she was incorporated by this sacrament of water and the Holy Spirit.