Millions of workers in the United States experience volatile weekly working hours and nonstandard shift work, particularly following the Great Recession. These aspects of work schedules bring greater economic insecurity and work-life conflict, particularly for low-wage workers. In the absence of strong and widespread policies regulating work hours in the United States, labor unions may significantly limit varying hours and nonstandard shifts. However, any benefits of union membership could depend on local unionization rates, which vary widely between states. This paper analyzes the relationship between union membership and varying weekly work hours and nonstandard schedules among hourly workers using data from the 2004–2007 and 2008–2012 Surveys of Income and Program Participation. The results show that union members were significantly less likely to report varying numbers of hours from week to week, particularly in states with relatively high unionization rates. In contrast, union members were more likely to report nonstandard schedules. The earnings penalties for varying hours and nonstandard schedules are significantly weaker among union members than non-members. Altogether, the results demonstrate some of unions’ continued benefits for workers, and some of their limitations.