Catechism of the Catholic Church
401 - The seventh commandment forbids unjustly taking or keeping the goods of one's neighbour and wronging him in any way with respect to his goods. It commands justice and charity in the care of earthly goods and the fruits of men's labour. For the sake of the common good, it requires respect for the universal destination of goods and respect for the right to private property. Christian life strives to order this world's goods to God and to fraternal charity.
2425 - The Church has rejected the totalitarian and atheistic ideologies associated in modem times with “communism” or “socialism”.
Leo XIII - Rerum Novarum
19 - The great mistake made in regard to the matter now under consideration is to take up with the notion that class is naturally hostile to class, and that the wealthy and the working men are intended by nature to live in mutual conflict. So irrational and so false is this view that the direct contrary is the truth. Just as the symmetry of the human frame is the result of the suitable arrangement of the different parts of the body, so in a State is it ordained by nature that these two classes should dwell in harmony and agreement, so as to maintain the balance of the body politic. Each needs the other: capital cannot do without labour, nor labour without capital. Mutual agreement results in the beauty of good order, while perpetual conflict necessarily produces confusion and savage barbarity. Now, in preventing such strife as this, and in uprooting it, the efficacy of Christian institutions is marvellous and manifold. First of all, there is no intermediary more powerful than religion (whereof the Church is the interpreter and guardian) in drawing the rich and the working class together, by reminding each of its duties to the other, and especially of the obligations of justice.
Pius XI – Quadragesimo Anno
120 - If Socialism, like all errors, contains some truth (which, moreover, the supreme pontiffs have never denied), it is based nevertheless on a theory of human society peculiar to itself and irreconcilable with true Christianity. Religious socialism, Christian socialism, are contradictory terms; no one can be at the same time a good Catholic and a true socialist.