The Decree Against Communism was a 1949 Catholic Church document issued by the Supreme Sacred Congregation of the Holy Office, and approved by Pope Pius XII, which declared Catholics who professed communist doctrine to be excommunicated as apostates from the Christian faith.

The document, as published in the Acta Apostolicae Sedis (see PDF below), bears the date July 1, 1949 and the heading Decretum (Decree), and is presented in the form of a dubium: that is, in question-and-answer format. It presents four questions, together with the Holy Office’s replies: (1) Is it licit to join or show favor to Communist parties? (2) Is it licit to publish, distribute, or read publications that support Communist doctrine or activity, or to write for them? (3) May Christians who knowingly and freely commit the acts in parts 1 and 2 be given the sacraments? (4) Do Christians who profess, defend, or promote materialistic Communist doctrine incur the penalty of excommunication as apostates from the Christian faith, with the penalty reserved so that it may only be lifted by the Holy See?

The answers in the decree were negative to the first three questions and affirmative to the fourth:

Q.1 Whether it is lawful to give a name to communist parties or to favor them.
        [By chance is it licit to give name or to make favors to communist parties?]

R. Negative: For communism is materialistic and anti-Christian; and the leaders of the communists, although they sometimes profess in words that they do not attack religion, yet, whether by doctrine or action, they show that they are seriously offended against God and true religion and the Church of Christ.

Q.2 Whether it is lawful to publish, propagate or read books, periodicals, diaries or newspapers, such as the doctrine or activity of the Communists, or to write in them.
       [By chance is it lawful to publish, promulgate or read books, journals or leaflets which defend the action or the communist doctrine, or to write for them?]

R. Negative: For they are forbidden by the very law.
        [Can Christians who perform the acts mentioned on n.1 and 2 be admitted to the sacraments?]

R. Negative, according to the ordinary principles of denying those sacraments, those who are not disposed to

Christi fideles, Who the materialistic and anti-Christian doctrine of the communists they profess, and in the first place, those who defend or propagate it, automatically, as apostates from the Catholic faith, incur the excommunication reserved in a special way to the Apostolic See.
       [If Christians declare openly the materialist and anti-Christian doctrine of the communists, and, mainly, if they defend it or promulgate it, “ipso facto”, do they incur in excommunication (“speciali modo”) reserved to the Apostolic See?]

R. Affirmative