RIVERSIDE (CBSLA.com) — Nurses and other Riverside County workers walked off the job at midnight over stalled contract negotiations.

Members of Service Employees International Union 721 — including health care, mental health and social workers, correctional officers, and engineers – picketed Wednesday at Riverside University Hospital in Moreno Valley.

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The union says talks broke down over safety issues, while the county declined to comment on why contract negotiations stalled.

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The county says it has temporary staffing to cover the strike, but will also ask a judge to declare the strike illegal.