18 Moreover, that the varied apostolates of the Church with respect to the media of social communication may be strengthened effectively, each year in every diocese of the world, by the determination of the Bishops, there should be celebrated a day on which the faithful are instructed in their responsibilities in this regard. They should be invited to pray and contribute funds for this cause. Such funds are to be expended exclusively on the promotion, maintenance and development of institutes and undertakings of the Church in this area, according to the needs of the whole Catholic world.
Source: Inter Mirifica (Vatican.va)