Which labor union was the largest outside supporter of the first Earth Day?

The United Auto Workers was the largest outside supporter of the first Earth Day.

Led by president Walter Reuther, the UAW provided unusually extensive financial, logistical, and organizational help for the April 22, 1970, event. Reuther made an early $2,000 donation, and the union helped fund telephone communication so organizers in different parts of the country could coordinate their activities.

The UAW also financed, printed, and mailed campaign literature and other materials. Its members participated in demonstrations, giving the environmental event support from organized labor as well as students, conservationists, and civic groups. Denis Hayes, the first Earth Day’s national coordinator, later described the UAW as the event’s largest contributor and said its absence might have caused the effort to fail.

A common mix-up is to choose a broad labor federation such as the AFL-CIO. The question asks for the particular union identified as the most instrumental outside financial and operational supporter: the United Auto Workers, commonly abbreviated UAW.