A labor strike is a work stoppage caused by a mass refusal of employees to work. Strikes are usually a response to grievances. Nearly 60,000 University of California workers represented by a pair of unions are striking due to ongoing contract negotiations. - Thousands of University of California employees, including physician assistants, optometrists, health care workers, and custodial staff, began a strike on Wednesday. - The workers are represented by two unions and are protesting alleged unfair labor practices and staffing shortages. - The strike is expected to last for multiple days, disrupting operations across the University of California system. - The unions are demanding better pay and more resources for their members. - Contract negotiations between the University of California and the unions are ongoing.