Final answer:
The Taft-Hartley Act is the law that addressed interstate transportation of strikebreakers and regulated union activities, including prohibiting the use of force or threats against union activities. Its comprehensive provisions transformed labor relations and restricted union powers in various ways.
Step-by-step explanation:
The law which prohibited the interstate transportation of strikebreakers for the purpose of using force or threats against union organizers, negotiators, or peaceful picketers is called the Labor Management Relations Act of 1947, commonly known as the Taft-Hartley Act. This piece of legislation was passed by Congress over President Truman's veto and restricted many powers of unions, leading to significant changes in labor law.
Notable provisions of the Taft-Hartley Act included banning closed shops and union shops, preventing secondary boycotts, requiring union leaders to disavow any communist affiliations, limiting the use of union funds in political campaigns, and permitting states to pass "right-to-work" laws.
The law also gave the President the power to delay a strike by imposing an 80-day "cooling-off period" to facilitate further negotiations without the immediate threat of work stoppages. This act notably reversed many of the advances made by labor unions in the first half of the twentieth century, impacting labor-management relations significantly.