The correct answer is A. National Labor Relations Act.
The National Labor Relations Act, passed in 1935, is a federal law that gave private sector employees significant rights in the work place. These rights include the ability to join a union without penalty, the ability to collectively bargain with their employers over wages, and the opportunity to take collective action (like striking) against their employers if the conditions/wages are not up to par. This was history in the making, as laborers had been fighting for legal rights like this since the late 19th century.