How have unions have changed over the years

What are the similarities and differences in the relationship with their employer/principal as it relates to agency?

How is the Independent Contractor-Employer Relationship the same as the Principal-Agent Relationship?  How is it different?

Consider how unions have changed over the years and whether it is simply a matter of time before all states are “right-to-work” states or whether unions will grow in stature and strength in the years to come.