More than 24,000 nurses and other health care workers at Kaiser Permanente in California and Oregon have overwhelmingly authorized a strike, threatening to walk out over pay and working conditions strained by the coronavirus pandemic.

Kaiser, one of the nation’s largest health care providers, has proposed a two-tiered wage and benefits system that would give newer employees lower pay and fewer health protections. The unions want Kaiser to abandon that plan. They also want 4% raises for each of the next three years and a commitment to hire more nurses to relieve staffing shortages. Kaiser has offered 1% a year, with additional lump sums, and says it must reduce labor costs to remain competitive.

The regional strike vote comes amid national contract negotiations between Kaiser and the Alliance of Health Care Unions, which represents more than 20 unions covering more than 50,000 Kaiser workers nationwide. More strike authorizations could come in Colorado, Georgia, Hawaii, Maryland, Virginia, Washington state and the District of Columbia, the unions said.

 This weekend’s votes don’t automatically trigger work stoppages. The union must give Kaiser Permanente 10 days’ notice before workers walk off the job, and both sides continue bargaining after their last contract expired on Sept. 30.