Clearly, unionization rates in the United States and Canada have diverged considerably since 1970. The question is, why?
Kris Warner [pdf] discusses a variety of possible explanations, from structural changes to the economy through the desire for unionization on the part of workers to the failures of organized labor itself. Warner then focuses on a key factor: employer opposition to unions together with relatively weak labor law.
the legal process for unionization and first contract arbitration are perhaps the most important policy differences, and illustrate the vast difference in labor policy between the United States and the country most similar to it. Compared to Canada, many workers in the United States are not able to exercise their right to freely join and form unions and participate in collective bargaining, in large part due to employer opposition, which current labor policy fails to adequately address.
The situation in the United States is even worse when compared to 21 other advanced capitalist countries, especially when taking into account union coverage rates: