A labor strike at the University of California Monday caused medical centers to reschedule more than 12,000 surgeries, cancer treatments and appointments.

Twenty-thousand members of the school’s largest employee union, the American Federation of State, County and Municipal Employees, staged a walk out and plan to strike for three days, according to The Los Angeles Times. Workers wore green union T-shirts and carried signs reading “We run UC.”

The strike is set to increase by 14,000, as members of the California Nurses Association will also join the walkout. Another 15,000 members of the University Professional & Technical Employees, who include pharmacists, clinical social workers, physical therapists, physician assistants and researchers will also be joining the strike, according to The LA Times.

The union’s spokesman John de los Angeles said the point of the strike was to highlight inequality and he believes the workers have sent a “clear message” to the school’s administration.

“The strong showing sent a clear message to administrators that our workers are very concerned about inequity and they’re willing to be on the picket line until UC comes up with a proposal to address their concerns,” he told The LA Times.

“Unfortunately, the only thing union leaders accomplished today is hurt the care we provide our patients and the services for our students,” UC spokeswoman Claire Doan said in an email to the LA Times Monday. “It will do nothing to change UC’s position on AFSCME’s unreasonable demands for excessive raises and benefits.”

UC’s five medical centers have hired workers to fill in for the striking union members, but have had to work to reschedule thousands of exams. UC San Francisco has now rescheduled over 12,000 appointments for surgeries and treatments, including radiation and chemotherapy,” according to The LA Times.