Which Act established that employers cannot force employees into contracts to retain their jobs?

The Noris LaGuardia Act of 1932 is significant because it protects the rights of workers to engage in union activities and prohibits employers from making contracts with employees that restrict their freedom to join labor organizations. This Act was a response to the aggressive tactics used by employers at the time, which often involved requiring employees to sign "yellow-dog" contracts—documents that stipulated they would not join a union as a condition of employment. By making such contracts unenforceable, the Noris LaGuardia Act bolstered the position of workers and aimed to level the playing field between employees and employers.

The other Acts mentioned have different focuses: the Taft-Hartley Act and the Labor Management Relations Act both relate to the regulation of labor unions and employer-employee relations but do not specifically prohibit the practice of requiring contracts for job retention. The Fair Labor Standards Act primarily addresses wage standards and does not pertain directly to the issue of job contracts and union membership rights. Thus, the Noris LaGuardia Act stands out as the correct choice for establishing the principle that employees cannot be forced into these restrictive contracts.