The Service Employees International Union and the California Nurses Association, two of the nation's biggest nurses' unions, are engaged in a slugfest over workers. The two unions are seeking to spoil each others' organizing drives with tactics such as ad campaigns, lawsuits, and infiltrating job sites. CNA says nurses would be better represented by a registered-nurses-only union that could focus on issues including nurse-to-patient staffing ratios. SEIU says nurses are better off in a bigger union that would also fight for other hospital workers and improve hospitalwide standards.