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Yes, barring perhaps some exceptional cases, a Catholic who becomes a Protestant is automatically excommunicated from the Church by Canon 1364 of the Code of Canon Law, because he or she professes heresy.Code of Canon Law:

an apostate from the faith, a heretic, or a schismatic incurs a latæ sententiæ* excommunication;

*i.e., excommunicated by the very act itself

Yes, barring perhaps some exceptional cases, a Catholic who becomes a Protestant is automatically excommunicated from the Church by Canon 1364 of the Code of Canon Law, because he or she professes heresy.

Yes, a Catholic who becomes a Protestant is automatically excommunicated from the Church by Canon 1364 of the Code of Canon Law:

an apostate from the faith, a heretic, or a schismatic incurs a latæ sententiæ* excommunication;

*i.e., excommunicated by the very act itself

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Yes, barring perhaps some exceptional cases, a Catholic who becomes a Protestant is automatically excommunicated from the Church by Canon 1364 of the Code of Canon Law, because he or she professes heresy.