The answer has changed over the years - depending on which political party is in power. Recently, the answer became "yes" again, and the facts may surprise employers as to what type of activity is protected.  In the recent case, a non-Union employee - acting alone -  stated at a company meeting that he and his coworkers shouldn't be working due to COVID risks.  The employee was later terminated. The National Labor Relations Board  (which is charged with protecting union rights) ruled that - even though the employee was acting alone - he had engaged in protected concerted activity during the meeting. Although "concerted activity" usually requires two or more employees working together to promote a union and/or improve working conditions - the Board found that this solo employee's complaint was still enough to be protected. Going forward employers should consider whether an employee's solo complaint - even in a non-union setting - may still be protected activity.