Adam Smith, Wealth of Nations, "The exclusive privileges of corporations, statutes of apprenticeship, and all those laws which restrain, in particular employments, the competition to a smaller number than might otherwise go into them, have the same tendency, though in a less degree. They are a sort of enlarged monopolies, and may frequently, for ages together, and in whole classes of employments, keep up the market price of particular commodities above the natural price, and maintain both the wages of the labour and the profits of
the stock employed about them somewhat above their natural rate." p. 52, http://www.ibiblio.org/ml/libri/s/SmithA_WealthNations_p.pdf
