OAKLAND, Calif. (AP) — Nurses in California went on strike Thursday — some for the second time in three months — in the latest dispute between nurses and hospital management over health-care costs, staffing levels and sick leave.

The California Nurses Association — the union behind the one-day walkout — expected 6,000 nurses at nine hospitals in the San Francisco and Los Angeles areas to participate, although hospital officials said some workers had crossed the picket lines.

The strike followed a walkout called by the association on Sept. 22 and came on the same day that more than 1,000 nurses in New York City gave notice that they plan to go on strike in January.

Officials at the California hospitals said replacement nurses had been brought in and patient care was not immediately affected.

“Strikes are a last resort, but nurses will only strike if they want to make sure that patients have safe care every day,” said Charles Idelson, a spokesman for the association.

The San Francisco Bay area hospitals targeted by the nurses are controlled by Sutter Health. The nurses’ contract with Sutter expired about six months ago, and union officials have objected to changes in paid sick leave and health- care premiums proposed by Sutter.

In Southern California, nurses at Long Beach Memorial Hospital and adjoining Miller Children’s Hospital, which are not controlled by Sutter Health, have raised concerns about staffing levels they say don’t allow them to take meal and rest breaks.

In Oakland, dozens of nurses picketed outside Alta Bates Summit Medical Center. They chanted and carried signs that read “RNs on strike for patient care.”

Leslie Silket, 44, a registered nurse and union representative, said she had worked at the center for 21 years.

“Today’s strike is to let Sutter know that we are standing solid in solidarity to fight back their corporate greed,” she said. “We are fighting for our patients. We are fighting for our contract.”

Both hospital systems said they will lock out striking nurses for additional days because their contracts with replacement nurses require a minimum number of days of service.

Nurses at the Sutter hospitals will be allowed to return to work on Saturday, Garner said. Nurses at the Long Beach hospital will be allowed to return on Tuesday.

The Long Beach hospital hired 400 replacement nurses although about 78 percent of the nurses at bedsides Thursday were its own employees, hospital officials said.

“ Currently we’re fully staffed,” said Dr. Susan Melvin, the hospital’s associate chief medical officer. “Every center of care is open and running.”

Myra Gregorian, the hospital’s vice president of human resources, estimated the cost of the walkout, including the nursing replacement contract and additional security, will run in the millions of dollars.

She disputed the union’s claims about staffing, saying the hospital complies with all state staffing ratios.