In general, concerted activity takes place when employees act as a group (in concert) for their mutual aid or protection. This includes activities like discussing the terms and conditions of their employment, such as pay, benefits, treatment by management, dress codes, workplace policies, or scheduling.
This activity—when engaged in by non-supervisory employees—is protected by Section 7 of the National Labor Relations Act. That means employers are legally prohibited from trying to stop employees from engaging in concerted activity or taking adverse action when they do. While supervisors don’t have these protections under Section 7, the term supervisor has a narrower definition than you might expect. To be exempt, supervisors must have real authority and use their independent judgment when wielding it. For instance, the 19-year-old assistant manager who is technically in charge when other supervisors are on break, but who doesn’t have the power to fire, discipline, or respond to the grievances of other employees, almost certainly still has protections under Section 7.
Employers should also be aware that it’s fairly easy for an employee to be protected under the act if they are discussing the terms and conditions of their employment either physically around co-workers or managers or in the same virtual space as co-workers or managers. While an employee may not be intending to act in concert for the mutual aid of themselves and their coworkers, if they post on Facebook about how they are overworked and underpaid, and several colleagues chime in that they agree, or even just “like” the post, that can become protected concerted activity.