Canon 2335 - Those who join a Masonic sect or other societies of the same sort, which plot against the Church or against legitimate civil authority, incur ipso facto an excommunication simply reserved to the Holy See.
After the Council, of course, the modernists desperately wanted to see the prohibition lifted so their allies could join them in their planned destruction of the Church.
This led to conflicting views from different Bishops' Conferences, with the Nordic Bishops allowing converts to retain their membership in the Lodge and the German Episcopate denouncing it.
In 1974, a private clarification, written to some episcopal conferences, was leaked. It had been interpreted by some within the Church as permitting Catholics to join Masonic lodges so long as the lodge did not directly plot against the church.
This led to the 1981 CDF Clarification Concerning Status of Catholics Becoming Freemasons:
On 19 July 1974 this Congregation wrote to some Episcopal Conferences a private letter concerning the interpretation of can 2335 of the Code of Canon Law which forbids Catholics, under the penalty of excommunication, to enroll in Masonic or other similar associations.
Since the said letter has become public and has given rise to erroneous and tendentious interpretations, this Congregation, without prejudice to the eventual norms of the new Code, issues the following confirmation and clarification:
1) the present canonical discipline remains in full force and has not been modified in any way;
2) consequently, neither the excommunication nor the other penalties envisaged have been abrogated;
3) what was said in the aforesaid letter as regards the interpretation to be given to the canon in question should be understood – as the Congregation intended – merely as a reminder of the general principles of interpretation of penal laws for the solution of the cases of individual persons which may be submitted to the judgment of ordinaries. It was not, however, the intention of the Congregation to permit Episcopal Conferences to issue public pronouncements by way of a judgment of a general character on the nature of Masonic associations, which would imply a derogation from the aforesaid norms.
Rome, from the Office of the S. Congregation for the Doctrine of the Faith, 17 February 1981.Franjo Cardinal Seper
Finally, in the 1983 Code of Canon Law, the express prohibition by name was removed, as follows:Canon 1374 - A person who joins an association which plots against the Church is to be punished with a just penalty; one who promotes or takes office in such an association is to be punished with an interdict.
It has been asked whether there has been any change in the Church's decision in regard to Masonic associations since the new Code of Canon Law does not mention them expressly, unlike the previous Code.
This Sacred Congregation is in a position to reply that this circumstance is due to an editorial criterion which was followed also in the case of other associations likewise unmentioned inasmuch as they are contained in wider categories.
Therefore the Church's negative judgment in regard to Masonic association remains unchanged since their principles have always been considered irreconcilable with the doctrine of the Church and therefore membership in them remains forbidden. The faithful who enrol in Masonic associations are in a state of grave sin and may not receive Holy Communion.
It is not within the competence of local ecclesiastical authorities to give a judgment on the nature of Masonic associations which would imply a derogation from what has been decided above, and this in line with the Declaration of this Sacred Congregation issued on 17 February 1981 (cf. AAS 73 1981 pp. 240-241; English language edition of L'Osservatore Romano, 9 March 1981).
In an audience granted to the undersigned Cardinal Prefect, the Supreme Pontiff John Paul II approved and ordered the publication of this Declaration which had been decided in an ordinary meeting of this Sacred Congregation.
Rome, from the Office of the Sacred Congregation for the Doctrine of the Faith, 26 November 1983.
Joseph Card. RATZINGER
+ Fr. Jerome Hamer, O.P.
Titular Archbishop of Lorium