In California, many councils have voted to raise the minimum hourly wage for workers. However, there is a loophole in these agreements that sometimes prevent unionized workers from benefitting from the same wage increase as everyone else. These types of exemptions do not exist in federal and state level minimum wages, but because cities in California are raising wages on their own, some of these loopholes are appearing. Workers, who at times pay over $50 a month in union fees could now be making less than their non-unionized coworkers.
See "Outrage After Big Labor Crafts Law Paying their Members Less than Non-Union Workers", Peter Jamison, The Los Angeles Times, April 11, 2016