The past two weekends, we have seen NFL players link arms in solidarity. They protest mistreatment and injustice in society, not mistreatment and injustice by their employers. In fact, there have been several instances where owners and coaches have joined in.
Had the players been protesting actions by their employers — their teams — their actions likely would be considered “protected concerted activity” under the National Labor Relations Act (NLRA). The NLRA grants employees the right to act collectively to protest terms or conditions of their employment. Employees have these rights even if there is no union.