The industrial umpire said it was satisfied the action, which has closed over 900 hospital beds since Saturday, is affecting the health, welfare and safety of patients.
The parties will have 90 days to attempt to reach a negotiated settlement.
The industrial action is part of the Australian Nursing Federation's campaign for better pay and conditions, including an 18.5 per cent pay rise over three years and eight months and the preservation of nurse-patient ratios.
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Victorian Hospitals Industrial Association chief executive Alec Djoneff said there were rumours the nurses would defy Fair Work Australia and continue with unprotected industrial action, as they had in 2007.
"Conciliation will not be easy," he told AAP.
