Populorum Progressio §58

⁵⁸ It is evident that the principle of free trade, by itself, is no longer adequate for regulating international agreements. It certainly can work when both parties are about equal economically; in such cases it stimulates progress and rewards effort. That is why industrially developed nations see an element of justice in this principle. But the case is quite different when the nations involved are far from equal. Market prices that are freely agreed upon can turn out to be most unfair. It must be avowed openly that, in this case, the fundamental tenet of liberalism (as it is called), as the norm for market dealings, is open to serious question.