During the industrial revolution the workers were treated bad. They got lower wages just because they were that desperate for work. Some workers would have worked whatever hours for whatever pay to provide for their families. Some of the workers were unskilled in the job so had a very low pay whereas the more skillful workers got paid a little bit more. Women got paid sometimes 1/3 that of a mans pay. Children even less then everyone.
The labor unions were seen as dangerous mostly because it could put some of the other workers in a tough position to pick sides. As far as benefits go though, unions help get more pay and better treatment.