U.S. oil workers have launched their largest strike in 35 years amid demands for safer conditions, higher pay and better healthcare. Nearly 4,000 members of the United Steelworkers Union walked off the job Sunday at nine sites which supply about 10 percent of the country’s refining capacity. One refinery in California has shut down, while managers have taken over operations at several other sites. The strike comes after union negotiators rejected an offer from Shell, which is leading contract talks on behalf of major firms including ExxonMobil, BP and Chevron. United Steelworkers says the oil industry is “the richest in the world” and can afford to address issues including unsafe staffing levels and dangerous conditions which lead to fires, explosions and leaks.