8 From this it is clear that legitimately constituted authority has the right and therefore the duty to restrict, to prevent, and to punish those base unions which are opposed to reason and to nature; but since it is a matter which flows from human nature itself, no less certain is the teaching of Our predecessor, Leo XIII of happy memory: "In choosing a state of life there is no doubt but that it is in the power and discretion of each one to prefer one or the other: either to embrace the counsel of virginity given by Jesus Christ, or to bind himself in the bonds of matrimony. To take away from man the natural and primeval right of marriage, to circumscribe in any way the principal ends of marriage laid down in the beginning by God Himself in the words 'Increase and multiply,' is beyond the power of any human law."
Source: Casti Connubii (Vatican.va)