The United Steelworkers union asked union workers at nine U.S. refineries to stop working after a national contract covering dozens of oil facilities expired on Monday. Take a look back at the 10 biggest strikes in U.S. history.
1. Great Southwest Railroad Strike -- In March 1886, the Knights of Labor went on strike over unsafe work conditions and unfair hours and pay at the Union Pacific and Missouri Pacific railroads, affecting 200,000 workers in five states. Nonunion workers and violence and scare tactics forced an end to the strike in September that year.