In an echo of a similar move following a strike in September, Sutter has brought in replacement nurses on five-day contracts and will not allow the striking nurses to return to work until Saturday morning. The replacement nurses will be paid for five days but will only work two days, officials said.
Thursday's strike saw about 90 percent participation among the approximately 4,000 nurses represented by the California Nurses Association at the affected hospitals, according to union spokesman Charles Idelson.
The union called the strike to protest concessions demanded by Sutter in five contracts currently under negotiation.
Sutter officials on Thursday said they saw a "significant percentage" of union-represented nurses report to work during the strike.
The health care organization reported that 63 percent and 59 percent of nurses reported to work at Antioch's Sutter Delta Medical Center and Castro Valley's Eden Medical Center, respectively, but that figure was only 16 percent at Sutter Solano Medical Center.
Idelson said the union had offered to call off the strike, which was announced several weeks ago, if the company backed off on some of the concessions it is asking in negotiations, but Sutter had declined.
Carolyn Kemp, spokeswoman for Alta Bates Summit hospitals in Oakland and Berkeley, said the two sides had met to negotiate twice this week and were expected to resume talks in the second week of January.
Kemp on Thursday said Summit is asking nurses to make co-payments for their health care coverage. She noted that nurses earn an average of $136,000 per year, and that nurses at Alta Bates Summit campuses have received a 22 percent salary increase over the last three years.
Idelson on Thursday said Sutter is now demanding fewer concessions than it was initially, but described the progress as "minute."