23 And now We wish to speak to rulers of nations. To you most of all is committed the responsibility of safeguarding the common good. You can contribute so much to the preservation of morals. We beg of you, never allow the morals of your peoples to be undermined. The family is the primary unit in the state; do not tolerate any legislation which would introduce into the family those practices which are opposed to the natural law of God. For there are other ways by which a government can and should solve the population problem—that is to say by enacting laws which will assist families and by educating the people wisely so that the moral law and the freedom of the citizens are both safeguarded.
Source: Humanae Vitae (Vatican.va)