As National Football League team owners consider President Trump’s call to fire players who refuse to stand for the national anthem, they have stumbled into one of the most consequential debates in today’s workplace: How far can workers go in banding together to address problems related to their employment?

In principle, the answer in the N.F.L. and elsewhere may be: Quite far.

To the extent that most people think about the reach of federal labor law, they probably imagine a union context — like organizing workers, or bargaining as a group across the table from management.

As it happens, the law is much more expansive, protecting any “concerted activities” that employees engage in to support one another in the workplace, whether or not a union is involved. The National Labor Relations Board and the courts have defined such activity to include everything from airing complaints about one’s boss through social media to publicly supporting political causes that have some bearing on one’s work life.

The league’s operations manual says players must be on the sidelines during the anthem and should stand. While the law might not bear on whether an individual player can kneel during the anthem, many experts say it could protect players from repercussions for making such a gesture together — or taking other action — to show solidarity on the job.