Employees at Kaiser Permanente, the biggest non-profit health care organization in the U.S., initiated a strike on Wednesday. This action was prompted by failed negotiations over staffing issues between the company and union representatives. In a matter of hours, over 75,000 unionized members are expected to join the strike, making it the most significant healthcare workers’ strike in U.S. history, as highlighted by the Coalition of Kaiser Permanente Unions.

Kaiser facilities in states including California, Colorado, Oregon, Virginia, Washington, and the District of Columbia will be affected by this strike. The walkout started at 6 a.m. ET in Virginia and D.C., with workers in other states set to join at 6 a.m. their local time.

The array of professionals participating in the strike spans a wide range of roles, including vocational nurses, emergency room technicians, radiology and X-ray techs, respiratory therapists, medical assistants, pharmacists, among several others.

Kaiser Permanente caters to almost 13 million patients, overseeing 39 hospitals and over 600 medical offices spread across eight states and the District of Columbia. In anticipation of the strike, Kaiser has made arrangements to ensure that patient care is not disrupted.