The United Steelworkers union, which represents employees at more than 200 U.S. oil refineries, terminals, pipelines and chemical plants, began a strike at nine sites on Sunday, the biggest walkout called since 1980. The USW started the work stoppage after failing to reach agreement on a labor contract that expired Sunday, saying in a statement that it “had no choice.” The union rejected five contract offers made by Royal Dutch Shell Plc on behalf of oil companies including Exxon Mobil Corp. and Chevron Corp. since negotiations began on Jan. 21. The steelworkers’ union hasn’t called a strike nationally since 1980, when a stoppage lasted three months. A full walkout of USW workers would threaten to disrupt as much as 64 percent of U.S. fuel production. Shell and union representatives began negotiations amid the biggest collapse in U.S. oil prices since 2008. “The problem is that oil companies […]