An official UC-wide strike notice for May 21-22 has been issued by AFSCME. The basic reasons are spelled out in a video by Kathryn Lybarger, President of AFSCME Local 3299, and an article by Lybarger for the SF Examiner. Quote:

UC medical centers grossed $6.9 billion last year — up more than 16 percent from three years ago — and banked hundreds of millions in profits. So where is all that money going?

Since 2009, “management” payroll at UC Health Facilities has grown by $100 million. Hospital CEOs have seen raises as big as $100 an hour, plus hundreds of thousands of dollars in bonuses. Debt payments for new facilities in San Francisco, San Diego and elsewhere have quadrupled, to the tune of hundreds of millions of dollars per year.
New UC policies have given hospital executives incentives to maximize revenues and cut costs without meaningful oversight. Too often, the cuts disproportionately impact patient care.

This includes dramatic increases in the use of undertrained temporary workers and volunteers for frontline care. It means fewer nursing aides often sharing responsibility for a larger number of patients. And for those who staff everything from surgical teams to cleaning crews, it means growing pressure to do their jobs faster and with fewer people.

UCSC maintains an information page regarding the strike.