What legislation protects the rights of employees to act together to improve their pay and working conditions, with or without a labor union?

The National Labor Relations Act is the legislation that specifically protects the rights of employees to act together to improve their pay and working conditions, whether or not they are part of a labor union. This act, also known as the Wagner Act, was enacted in 1935 to encourage collective bargaining and to protect the rights of employees to organize. It establishes the right for workers to engage in "concerted activities," which are actions taken together to improve their working conditions or to address grievances.

This legislation provides a framework for employees to collectively negotiate with employers and ensures that employers cannot retaliate against employees for participating in such joint efforts. The act also created the National Labor Relations Board (NLRB), which oversees and enforces these rights.

While other acts mentioned in the options pertain to specific aspects of employment law—such as wage standards, workplace safety, or labor relations—they do not encapsulate the broader rights to collective action as established by the National Labor Relations Act.