Tens of thousands of Kaiser Permanente's California workers have signed a petition to leave United Healthcare Workers West and join the newly formed National Union of Healthcare Workers. The 50,000-employee bargaining unit is one of the largest among the nation's private-sector employers, and taking it over would be a significant coup for the NUHW. The group was created last month by former leaders of the UHW after the Oakland-based local was placed under trusteeship by its parent organization, the Service Employees International Union.