21 It is furthermore the duty of the State to ensure that terms of employment are regulated in accordance with justice and equity, and to safeguard the human dignity of workers by making sure that they are not required to work in an environment which may prove harmful to their material and spiritual interests. It was for this reason that the Leonine encyclical enunciated those general principles of rightness and equity which have been assimilated into the social legislation of many a modern State, and which, as Pope Pius XI declared in the encyclical Quadragesimo Anno , (8) have made no small contribution to the rise and development of that new branch of jurisprudence called labor law.
Source: Mater et Magistra (Vatican.va)