They gathered outside the Unique Thrift Store in Chicago's Uptown neighborhood. Workers say they have no safety equipment while sorting donations and claim fire doors are often blocked.
Employees say they want to earn more than minimum wage.
The owners of Unique Thrift Store issued the following statement on Monday night: "We regret that our employees are being misled by a large international labor union disguising themselves as a local community group in support of Hispanic workers in an effort to unionize our store. Given the union's claims, we find it interesting that information and flyers offered to store employees were provided in English only – not Spanish. We are aware that a petition for election was signed and filed with the National Labor Relations Board by a senior and highly-paid official of the Service Employees International Union. We support our employees' right to decide, and will provide our employees with the information necessary to cast an informed ballot in the secret ballot vote that the National Labor Relations Board has scheduled for December 4, 2013."