21 Nor is the benefit that has poured forth from Leo's Encyclical confined within these bounds; for the teaching which On the Condition of Workers contains has gradually and imperceptibly worked its way into the minds of those outside Catholic unity who do not recognize the authority of the Church. Catholic principles on the social question have as a result, passed little by little into the patrimony of all human society, and We rejoice that the eternal truths which Our Predecessor of glorious memory proclaimed so impressively have been frequently invoked and defended not only in non-Catholic books and journals but in legislative halls also courts of justice.
Source: Quadragesimo Anno (Vatican.va)