Unions traditionally emphasize fairness, objectivity, and equal treatment when negotiating employment conditions. According toHuman Resource Management, 16th Editionby Gary Dessler,seniorityis the factor unions most strongly prefer when determining criteria for promotions, layoffs, recalls, and job security.
Seniority systems are favored because they are objective, easy to verify, and limit managerial discretion, which unions often view as a potential source of favoritism or discrimination. By basing decisions on length of service, unions help ensure predictability and transparency in employment decisions, protecting long-term members from arbitrary treatment.
Dessler notes that while employers may prefer performance- or skill-based systems to reward high performers, unions typically resist these approaches unless they are clearly defined and consistently applied. Education and experience may be considered in some agreements, but seniority remains the dominant standard in unionized settings. Age, while correlated with seniority, is not used directly due to legal and ethical concerns.
Therefore, the correct answer isseniority.
Source:
Gary Dessler,Human Resource Management, 16th Edition, Chapter on Labor Relations and Collective Bargaining