Proponents of ILMS argued that the existence of dual labor markets, especially its primary component, did not fit well within the orthodox model of pure competition determining wages. The idea that labor mobility would lead to a reduction in wage differentials was flawed, if not altogether wrong, because of the discriminatory barriers that faced blacks, other ethnic minorities, and women. When it came to the subject of unions however, Piore and Doeringer's ILMS model encountered difficulty in explaining how supposedly secondary labor markets were able to transform themselves into primary markets through unionizing efforts. Nor were they ever able, like older institutionalist labor economists, to ultimately reject the overriding authority of marginal productivity theory.
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