Mater et Magistra §18

¹⁸ They concern first of all the question of work, which must be regarded not merely as a commodity, but as a specifically human activity. In the majority of cases a man's work is his sole means of livelihood. Its remuneration, therefore, cannot be made to depend on the state of the market. It must be determined by the laws of justice and equity. Any other procedure would be a clear violation of justice, even supposing the contract of work to have been freely entered into by both parties.