Labor law (or labor relations law) is the law governing relations between employees acting as a group, unions, and employers.
"Many times, those employees will have chosen a labor organization—a union—to represent them collectively. But all employees have rights under labor law to engage collective action for mutual gain, whether or not they are represented by, or have any interest in joining, a union." Samuel Estreicher & Matthew T. Bodie, Labor Law 1 (2016).