Henning served 26 years as executive secretary-treasurer of the California Labor Federation, AFL-CIO, which represents more than 2 million workers.
Henning's health had been deteriorating for years, said Art Pulaski, the union's executive secretary-treasurer. Pulaski said he was notified of the death Thursday by Henning's son, Pat.
Henning served as undersecretary of labor under President Kennedy and later was appointed by President Johnson as U.S. ambassador to New Zealand.
After returning to California, Henning helped the United Farm Workers campaign for passage in 1975 of the state Agricultural Labor Relations Act.