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.
9. 1970 U.S. Postal Service strike -- This strike started in New York City but spread to 210,000 postal workers nationwide in March 1970 over increased dissatisfaction with wages, working conditions, benefits and management. Their demands were largely met after mail delivery came to a near standstill.