This week, Democratic presidential hopeful Bernie Sanders unveiled a plan to double membership in unions by making it easier for workers to organize. Several other Democratic candidates are promising policies to revive labor unions, too. Union membership has declined dramatically over the past several decades in the United States, from a high of about one-third of workers in the postwar era to just 6% today. The bulk of those losses have been seen in private sector unions.

A new report from the Brookings Institution explores what’s contributed to the decline and how unions’ diminishing power affects all workers. Union members earn 15% to 20% more than equivalent workers at nonunion shops, and as membership has shrunk, wage growth for low- and middle-rung workers has stalled and income inequality has grown.

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