In terms of members, the public unions have as many members as private sector unions. In fact, the public sector unions have been growing while the private sector unions have been shrinking.
“The number of employed union members has declined by 2.9 million since 1983. During the same time, the number of all wage and salary workers grew from 88.3 million to 133.7 million. Consequently, the union membership rate was 20.1 percent in 1983 and declined to 11.1 percent in 2015.”