The National Union of Healthcare Workers called for the strike. The union represents about two dozen mental health and optical workers at Kaiser in Fresno.
A representative says they're just fighting to keep their health and retirement benefits and to help improve patient care.
The California Nurses Association, which represents about 500 nurses in Fresno - told its members to join the strike if they want to.
"The message is that they're not listening to us at the bargaining table," said Dennis Lewis. "But, more importantly, they're not listening to patients."
Amy Tobin, lead nurse said, "So our staff, who do choose to come to work, will be assigned according to their competency level."
Kaiser says all of its locations will be open Thursday, and patients will be able to receive full care during work stoppage.