Why has union membership fallen in the last 20 years?
There are many factors affecting union membership in both the public and private sector.
The first reason for the decline in union membership is that many of the jobs that were traditionally unionized in developed countries have either been outsourced to the developing world or become technologically obsolete.
Next, regulatory changes, especially what are euphemistically called "right to work" laws in various states have created barriers to unionization.
Another major factor is outsourcing of work and increase in temporary and contract employment. Rather than hire well-paid long-term unionized employees, employers increasingly rely on cheap contract labour, or contract workers hired from agencies to reduce costs.