There is a growing movement to raise the wages of fast food workers, with the rallying cry of $15 an hour. The protests come in the backdrop of a national push for a higher minimum wage, but are focused on one of America's largest low-wage industries.

A new study of Oakland workers shows exactly how low the wages are in the fast food industry. Restaurant Opportunites Center United conducted a survey of 500 restaurant workers from August 2013 to July 2014 and found that 36 percent did not make enough money to buy food for themselves and their families, while more than half said they were eating free meals at their jobs only because they couldn't afford to pay for their own food.

The survey found that the median wage paid to the workers was $9 an hour; Oakland voters will have the opportunity to approve a $12.25 minimum wage via ballot referendum in November.