Final answer:
The Taft-Hartley Act of 1947 imposed significant restrictions on labor unions' ability to strike, including banning closed and union shops, introducing a presidential intervention option for strikes affecting national interests, and outlawing secondary boycotts.
Step-by-step explanation:
The Taft-Hartley Act of 1947 significantly amended the Wagner Act by introducing measures that restricted the abilities and powers of labor unions. One of these measures was the ability to use strikes as bargaining tools. The act banned both closed shops, where only union members could be hired, and union shops, which required new employees to join a union after a certain amount of time.
Furthermore, it prohibited secondary boycotts and mandated that union leaders swear they were not affiliated with any communist organizations. It also allowed for presidential intervention to delay strikes that could impact national health or safety for up to 80 days, a provision that was employed by President Obama in 2015 during the longshoremen labor dispute.