Among occupational groups, protective service had the highest union membership rate in 1999, at 38.2 percent.
The unionization rate for protective service occupations—which include police officers, prison guards, and firefighters—was well above the average of 13.9 percent for all occupations. Other occupational groups with higher-than-average unionization rates were precision production, craft, and repair workers (22.4 percent); operators, fabricators, and laborers (20.7 percent); and professional specialty (19.7 percent).
At 4.1 percent, the lowest union membership rate was in sales occupations. The unionization rates were also under 10 percent in executive, administrative, and managerial jobs and in service occupations other than protective service.
Bureau of Labor Statistics, U.S. Department of Labor, The Economics Daily, Protective service occupations have highest union membership rate at https://www.bls.gov/opub/ted/2000/jan/wk3/art03.htm (visited November 29, 2022).