The fourth principal HRM function is maintenance of human resources. This encompasses activities related to employee benefits, safety and health, and worker-management relations. Employee benefits include health insurance and parking to transfer non-taxed compensation. HRM managers administer three categories of benefits: employee services, vacations and absences, and insurance, retirement, and health benefits. Safety and health activities ensure compliance with laws protecting employees from workplace hazards. Maintenance of worker-management relations includes handling grievances, developing communication systems, and contract negotiation.