That article said nothing except that they are striking. Over what?
http://job-descriptions.careerplanner.com/Structural-Iron-and-Steel-Workers.cfm
“This work stoppage is about onerous overtime; unsafe staffing levels; dangerous conditions the industry continues to ignore; the daily occurrences of fires, emissions, leaks and explosions that threaten local communities without the industry doing much about it; the industry’s refusal to make opportunities for workers in the trade crafts; the flagrant contracting out that impacts health and safety on the job; and the erosion of our workplace, where qualified and experienced union workers are replaced by contractors when they leave or retire,” Beevers added.