As of 2015, in Hawai`i 20.4% of workers belong to a labor union and 21.7% of workers are represented by a labor union.  This is the second highest proportion of union participation in the United States.
History of Labor Organizing
In 1938, 70 police officers opened fire on 200 striking longshoreman at the port of Hilo, resulting in 50 injuries. 
In 1946, workers held a strike simultaneously at almost all the plantations on the island. This came to be known as the Hawaiian Sugar Strike.