9 In addition, another matter which is close to your hearts must be safeguarded. In fact, you have already sent a joint letter to the faithful. It is the cause of workers, who sorely need the support of religion both for the honorable accomplishment of their labors and for the alleviation of their sufferings. Their cause is closely connected with the social question; the more difficulties it encounters, the more pressing is its need for attention. If the bishops direct their attention to this question, if they see to it that justice and charity influence all classes of society and are deeply imprinted in souls, if by their authority and activity they come to the aid of the lowly condition of workers, they will have deserved well of the Church and society alike.
Source: In Ipso (Vatican.va)