Throughout the 1960s, Aaron helped mediate a large number of labor disagreements, including disputes between workers and employers in the transit, railroad transportation, longshore, aerospace, health care, airline and agricultural industries. He helped negotiate the first contract between a county and a public employee union in California history in 1968. He later assisted the County of Los Angeles in drafting a public employee collective bargaining ordinance, and served as the mediator during the first contract negotiations between the county and its public employee unions.