By Ahmed Aboulenein

(Reuters) -Tens of thousands of nurses and other healthcare workers launched a planned three-day strike at Kaiser Permanente facilities across the U.S. on Wednesday, after contract talks failed to meet the union deadline for reaching a settlement.

The strike against Kaiser, one of the nation's leading not-for-profit healthcare networks and managed-care organizations, marks the largest strike ever in the U.S. medical industry. Kaiser Permanente said its hospitals and emergency departments would remain open through the strike and staffed by doctors, managers and "contingency workers."

The tight U.S. labor market and inflation have led to contentious contract negotiations and strikes over pay and benefits for workers in numerous fields this year, including the automobile, rail, airline and entertainment industries.

The Kaiser union had set a deadline of 6 a.m. PDT (1300 GMT) Wednesday to reach a deal on a new pact covering nurses, medical technicians and support staff in hundreds of hospitals across California, Oregon, Washington state, Colorado, Virginia and Washington, D.C.

"Both Kaiser Permanente management and coalition union representatives are still at the bargaining table, having worked through the night in an effort to reach an agreement," Kaiser said in a statement Wednesday.

The coalition, made up of eight unions representing nurses, technicians and support staff, said the company has failed to negotiate in good faith in talks. The previous labor pact expired on Sept. 30.

Kaiser nationwide employs 68,000 nurses and 213,000 technicians, clerical workers, and administrative staff, alongside its 24,000 doctors.

The unions have been pressing for better wages and for Kaiser to fill more jobs. Staffing levels have been a major sticking point, with the union insisting Kaiser needs to hire 10,000 new healthcare workers to fill current vacancies.

In Virginia and Washington, D.C., only optometrists and pharmacists would be on strike, but the impact on patients in California, Colorado, Oregon, and part of southwestern Washington state would be more substantial, a Kaiser spokeswoman said Tuesday.

Nearly 309,700 workers have been involved in work stoppages through August this year, according to U.S. Bureau of Labor Statistics data, putting 2023 on track to become the busiest year for strikes since 2019.

(Reporting by Ahmed Aboulenein)