About 100 nurses at Petaluma Valley Hospital staged a one-day walk-out Wednesday, the first labor strike in the hospital's 30-year history.
The hospital responded by bringing in replacement nurses on five-day contacts, essentially locking out the union nurses for four days.
The members of the California Nurses Association said they were protesting significant cuts to stand-by pay for on-call nurses, as well as mandatory on-call scheduling they said threatens patient safety.
The union represents about 160 registered nurses at Petaluma Valley Hospital, which is operated by St. Joseph Health, Sonoma County.
St. Joseph officials said the hospital, with an in-patient load Wednesday of less than 40, was safely staffed with contract replacement nurses and some union nurses who crossed the picket line.