Should the minimum wage be lower for workers who get tipped? Two states are set to decide

Mel Nichols, a 37-year-old bartender in Phoenix, Arizona, takes home anywhere from $30 to $50 an hour with tips included. But the uncertainty of how much she's going to make on a daily basis is a constant source of stress.

“For every good day, there's three bad days,” said Nichols, who has been in the service industry since she was a teenager. “You have no security when it comes to knowing how much you're going to make.”

That uncertainty exists largely because federal labor law allows businesses to pay tipped workers, like food servers, bartenders and bellhops, less than the minimum wage as long as customer tips make up the difference. Voters in Arizona and Massachusetts will decide in November whether it's good policy to continue to let employers pass some of their labor costs to consumers.

The ballot measures reflect an accelerating debate over the so-called subminimum wage, which advocates say is essential to the sustainability of the service industry and detractors say pushes the cost of labor off employers' shoulders and leads to the exploitation of workers.