WASHINGTON—The share of American workers in labor unions fell to a fresh record low last year, despite an uptick in the ranks of unionized state-government employees.

The number of union members fell by 170,000 in 2019—a year when U.S. employers added more than 2.1 million jobs—reducing the share of the workforce in labor unions to 10.3%, the lowest portion on record since 1983, the Labor Department said Wednesday. Overall union membership rates have trended at record lows for a decade.

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