Under CPCU 500, risk sources are categorized to help risk professionals understand where uncertainty originates and how it may affect an organization. The major general categories include natural, human, economic, and catastrophic risk sources. The key to answering this question is identifying the direct source of the risk rather than its secondary effects.

Labor union strikes are the result of deliberate human actions arising from workplace negotiations, disputes, or collective bargaining decisions. The operational disruptions---such as halted production, supply chain interruption, reduced revenue, or contractual penalties---stem directly from decisions and behaviors of people. Therefore, strikes are classified as human risk sources.

Although strikes may produce financial consequences, they are not categorized primarily as economic risk sources. Economic risk sources relate to broader market forces such as inflation, interest rate changes, recessions, or currency fluctuations. Similarly, strikes are not natural risk sources, which involve perils like hurricanes, earthquakes, or floods. Nor are they typically catastrophic risk sources, which refer to large-scale events causing widespread devastation across regions or industries.

CPCU 500 emphasizes analyzing risk by tracing it back to its origin. Since a labor strike originates from organized human decision-making and behavior, its direct effects are properly classified under human risk sources.