A federal law that concerns itself with the relationships between a business firm and labor unions is?

The federal law that primarily governs the relationships between business firms and labor unions is the National Labor Relations Act (NLRA) of 1935. This law establishes the rights of employees to organize, engage in collective bargaining, and take collective action, while also outlining the responsibilities of employers and unions. It created the National Labor Relations Board (NLRB) to oversee and enforce these rights, aiming to promote fair labor practices and prevent unfair labor practices by both employers and unions.