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.”

The amount tipped workers make varies by state. Fourteen states pay the federal minimum, or just above $2 an hour for tipped workers and $7 an hour for non-tipped workers.