Not many workplaces where they play the national anthem before your shift.
But let's go ahead and follow out your logic. Two question comes to mind.
Who sets the rules in the workplace? The owners do sir.
And what rules are they violating?
1) None do but the NFL does. That's all that matters. The 1st Amendment doesn't apply to the workplace. End of story.
2) The boss does.
3) Until the boss says they can't do it, they can do it.
Just making the point the 1st Amendment is not in play in this situation.