This paper examines the link between stagnant wages and the increasingly concentrated power of large corporate buyers. With the rise of big-box retailers and other large intermediary purchasers, suppliers in industries like manufacturing and transportation, former bastions of middle-income employment, face pressure from buyers to reduce wages. Economic sociology predicts that buyer power can either decrease suppliers’ wages by destroying rents or increase wages by raising productivity through buyer-supplier collaboration. Panel analysis of data on publicly traded suppliers shows that supplier reliance on large buyers decreases suppliers’ wages. Instrumental variables analysis of mergers among buyers shows that these wage decreases result from increased buyer power. Increasing reliance on key buyers accounts for 10% to 15% of the decline in wage growth since 1978. These results show that the social structure of production markets can restrain wage growth.