More than 24,000 nurses and other health-care workers at Kaiser Permanente authorized a strike, their unions announced Monday, threatening to walk out over pay and working conditions while the coronavirus pandemic continues to strain hospitals and clinics.

Workers in California and Oregon endorsed the work stoppage by an overwhelming margin in the weekend vote as they pressed Kaiser to scrap its plans for a two-tiered wage and benefits system, which would pay newer employees less than more tenured colleagues and offers them fewer health protections. They also want 4 percent raises for the next three years and a commitment to hire more nurses to relieve staffing shortages.

Another 7,400 Kaiser employees, members of the United Steel Workers Local 7600, also voted to authorize the walkout.

More than 50,000 Kaiser workers nationwide are making similar demands in contracts that will soon expire, and union leaders say more strike authorization drives could materialize in Colorado, Georgia, Hawaii, Maryland, Virginia, Washington state and D.C.

The vote — approved by 96 percent of the union’s 21,000 members in California and 3,400 in Oregon after three days of electronic balloting — does not automatically trigger a work stoppage. The union must give Kaiser Permanente 10 days’ notice before workers walk off the job. Labor and business leaders both expressed hope that a resolution could be found at the bargaining table in the coming days, though union officials acknowledged the sides remain divided on key issues.

The looming impasse is another example in recent weeks of the labor movement’s increasingly hardened stance in contract negotiations. Hollywood production workers voted to authorize a strike earlier in October and workers at Kellogg’s cereal factories walked off workroom floors last week.

The leaders of the two unions that led the strike drive, the United Nurses Associations of California/Union of Health Care Professionals and Oregon Federation of Nurses and Health Professionals, say the pandemic has exposed systemic problems in the health-care workforce and that nurses and other health workers can no longer weather the long and debilitating hours without more corporate support.

“Our members feel that they’re pivotal stakeholders to how health care is administered and designed at a front-line level. We think it’s valuable work and we think it’s being cut back. We think systems have been shortchanged,” Denise Duncan, president of the California union and a registered nurse, told The Washington Post.

“There’s increased pressure placed on nurses for what we call the churn. Get the patient in and get the patient out,” Duncan said. “We need more hands on deck.”

A strike would affect hospitals in Anaheim, Bakersfield, Baldwin Park, Downey, Fontana, Irvine, Los Angeles, Ontario Vineyard, Panorama City, Riverside, San Diego, West Los Angeles and Woodland Hills in California. In Oregon, Kaiser facilities are generally concentrated in Portland, but facilities as far south as Eugene would also be affected.

Kaiser spokesman Marc Brown wrote in an emailed statement that the company was “committed to resolving this quickly” and would continue to negotiate with labor leaders. Kaiser workers are represented by individual trade unions, but they bargain on larger issues — such as wages and benefits — together as part of the Alliance of Health Care Unions.

“We ask that our employees reject a call to walk away from the patients who need them,” Brown said. “Our priority is to continue to provide our members with high-quality, safe care. In the event of any kind of work stoppage, our facilities will be staffed by our physicians along with trained and experienced managers and contingency staff.”

But union officials said Kaiser executives would be at fault for any work stoppage. More than 4 in 10 Kaiser health workers in Oregon reported considering leaving the health-care industry because of the company’s wage system and staffing issues, according to a survey conducted by the Oregon Federation of Nurses and Health Professionals.

“I think rich Kaiser executives should not exploit working people to make a profit,” Shane Burley, a communications organizer with the Oregon union, said in an interview. “When patients are upset about what’s happening in the health-care system, they should look at these big executives who are making big salaries and trying to cut costs by undermining working people and health-care professionals.”