Recognizing that the Church is the arbiter not only of Divine Revelation but of what God reveals through creation in what we call the Natural Law, I am more inclined to want to get the natural law right, to study Catholic social teaching with great care, and to develop a political party that combines the best and most comprehensive recognition of the corresponding principles that ought to animate both the social order and government itself.
Latins claim this as a part of the authority of the Church (see CCC 2036 and Dignitatis Humane 14), but where is the warrant within Apostolic Tradition? Setting aside those secondary precepts which are not directly directly through reasoning but are determined by reason or are applications of reason in finding a convention to order some state of affairs (e.g. driving on which side of the road), there are several points to be made.
1. There are precepts of Natural Law that have nonetheless been revealed directly by God as well. These have been passed down as a part of Sacred Tradition. So bishops can be said to be arbiters of the Natural Law, in so far as they have received it as a part of God's revelation to Israel and in Christ. But does that revelation include all possible secondary precepts?
2. Knowing apart from Divine Revelation the "fullness" of the Natural Law requires not intellectual virtue but moral virtue. Do bishops have a special charism from the Holy Spirit that replaces the need for this and the habit of synderesis and the logical reasoning required as well? This is a more dubious claim.
That the Church possesses the authority to teach the precepts of the Natural Law is probably a long-standing Latin theological opinion. (Going back to Trent if not some time before, during the medieval period?) I'd like to read a treatise or manual that show some nuance in presenting this. Can the patriarchate of Rome cite one of its "ecumenical councils" as an authority espousing this opinon? I am doubtful, since the CCC makes no such reference.
See the old
CE entry on the Natural Law.