160 It may sometimes happen, therefore, that meetings arranged for some practical end—though hitherto they were thought to be altogether useless—may in fact be fruitful at the present time, or at least offer prospects of success. But whether or not the moment for such cooperation has arrived, and the manner and degree of such co-operation in the attainment of economic, social, cultural and political advantages—these are matters for prudence to decide; prudence, the queen of all the virtues which rule the lives of men both as individuals and in society. As far as Catholics are concerned, the decision rests primarily with those who take a leading part in the life of the community, and in these specific fields. They must, however, act in accordance with the principles of the natural law, and observe the Church's social teaching and the directives of ecclesiastical authority. For it must not be forgotten that the Church has the right and duty not only to safeguard her teaching on faith and morals, but also to exercise her authority over her sons by intervening in their external affairs whenever a judgment has to be made concerning the practical application of this teaching. (67)
Source: Pacem in Terris (Vatican.va)