"God, the Lord of life, has entrusted, to men the noble mission of safeguarding life, and men must carry it out in a manner worthy of themselves. Life must be protected with the utmost care from the moment of conception: abortion and infanticide are abominable crimes."
Gaudium et Spes ,  51 (1966).

"Since the first century the Church has affirmed the moral evil of every procured abortion. This teaching has not changed and remains unchangeable. Direct abortion, that is to say, abortion willed as either an end or a means, is gravely, contrary to the moral law: You shall not kill the embryo by abortion and shall not cause the new born to perish."
Catechism of the Catholic Church (2271 ).

"The inalienable right to life of every innocent human individual is a constitutive element of a civil society and its legislation."
Catechism of the Catholic Church (2273 ).

"The inalienable rights of the person must be recognised and respected by civil society and the political authority. These human rights depend neither on single individuals nor on parents; nor do they represent a concession made by society and the state; they belong to human nature and are inherent in the person by virtue of the creative act from which the person took his origin. Among such fundamental rights one should mention in this regard every human person’s right to life and physical integrity from the moment of conception until death."
Congregation for the Doctrine of the Faith, Donum Vitae III (1987).

"The moment a positive law deprives a category of human beings of the protection which legislation ought to accord them, the state is denying the. equality of all before the law. When the state does not place its power at the service of the rights of each citizen, and in particular of the more vulnerable, the very foundations of a state based on law are undermined … As a consequence of the respect and protection which must be ensured for the unborn child from the moment of conception, the law must provide appropriate penal sanctions for every deliberate violation of the child’s rights."
Congregation for the Doctrine of the Faith, Donum Vitae III (1987).

"How can one morally accept laws that permit the killing of a human being not yet born, but already alive in the mother’s womb? The right to life becomes an exclusive prerogative of adults who even manipulate legislatures in order to carry out their own plans and pursue their own interests."
Letter to Families , John Paul II,  21 (1994).

Pope John Paul II's 1995 Encyclical Evangelium Vitae has a few long and important quotes on abortion and related issues. See  Evangelium Vitae, 58-62, 73.

"When – concerning areas or ‘realities that involve fundamental ethical duties – legislative or political choices contrary to Christian principles and values are proposed or made, the Magisterium teaches that 'a well-formed Christian conscience does not permit one to vote for a political programme or an individual law which contradicts the fundamental contents of faith and morals'."
Congregation for the Doctrine of the Faith, Doctrinal Notes on Some Questions Regarding the Participation of Catholics in Political Life , 4 (2002).

"Eucharistic consistency … Worship pleasing to God can never be a purely private matter ...This is true for all the baptised, yet it is especially incumbent upon those who, by virtue of their social or political position, must make decisions regarding fundamental values such as respect for human life, its defence from conception to natural death … These values are not negotiable. Consequently, Catholic politicians and legislators, conscious of their grave responsibility before society, must feel particularly bound, on the basis of a properly formed conscience, to introduce and support laws inspired by values grounded, in human nature. There is an objective connection here with the Eucharist."
Sacramentum Caritatis , Benedict XVI, 83 (2007).