CHICAGO -- About 500 workers employed by Edsal Manufacturing are on strike on Chicago's South Side. They walked off the job Monday in a dispute over wages.Edsal makes industrial shelving and storage systems in Chicago's Back of the Yards neighborhood.The workers are members of AFL-CIO Machinists Local 30. One worker said they are striking because they have not received a raise in more than 12 years.Officials with Edsal have not responded to ABC7's requests for comment.