More than 30,000 Kaiser Permanente nurses and health care workers across California are hitting the picket line Tuesday, as a five-day strike begins.

Workers with the United Nurses Associations of California / Union of Health Care Professionals (UNAC/UHCP) walked off the job beginning at 7 a.m. amid a dispute over staffing, pay and patient care. The union said the walkout is the largest strike in its history.

Along with nurses, the union represents pharmacists, nurse practitioners, midwifes, physician assistants, rehab therapists, speech language pathologists, dietitians and other specialty healthcare workers. 

A spokesperson for Kaiser Permanente in Northern California told CBS News Bay Area that pharmacists in the region are not striking and pharmacies are running normally.

In the San Francisco Bay Area, picket lines were expected at the Oakland Medical Center and Santa Clara Medical Center. The walkout also affects one facility in the Sacramento region, the Roseville Medical Center.  

Meanwhile in Southern California, picket lines were scheduled to take place at hospitals and medical offices in Bakersfield, Los Angeles County, Orange County, the Inland Empire and San Diego County. The strike also impacts three hospitals in Hawaii, two on the island of Oahu and one on the island of Maui.

"Our union made repeated attempts to reach a fair agreement. This dispute centers on staffing levels, respect for professional expertise, and patient safety — not just pay," the union said in a statement Monday. "This strike is about protecting the future of patient care."

The union is calling for a 25% wage increase over four years, arguing that wages have not kept up with inflation and that Kaiser gave other unions higher wage increases. Workers are also seeking changes to scheduling and staffing.

Kaiser Permanente said they are offering a 21.5% increase over four years, which the healthcare organization claimed was already above market wages.

"A strike is unnecessary when a generous offer is on the table. The strike is designed to disrupt the lives of our patients — the very people we are all here to serve," Kaiser said in a statement Monday.

The organization said it had prepared contingency plans in the event of a strike, saying hospitals and most medical offices will remain open. Up to 7,600 nurses, clinicians and other staff are being brought in to work at Kaiser facilities during the walkout.

During the strike, Kaiser said some appointments are being shifted to virtual visits, while other appointments, elective surgeries and procedures are being rescheduled.

The strike is set to end at 7 a.m. on Sunday.