Fellas I think we created a tyrant!
The Straight Dope really gets things done! 
It depends on if your workers are at-will employees. If you are a business owner or a boss I’m surprised you don’t know about at-will employment and the rules governing it in your state.
NFL players are not at-will employees since they work under a collective bargaining agreement. The personal conduct policy gives the league and individual teams the power to discipline for basically anything that makes them look bad. And also players can be cut for no reason at all. Neither has happened to Kaepernick and management has stated he is not violating any policy so the point is moot.
Oh, I know I can fire my employees any time I want, and for any reason I want, except in the cases of being fired for being a protected class. I just assumed that political affiliation was protected, I was surprised enough that I went back and looked at my labor law poster, because I was sure it was on it, I then checked my state labor law poster, in case it was at least protected at that level. I was mistaken in my assumption.
I probably got that assumption from watching The Good Wife. (And now that I think about it, that was an episode that involved someone let go from a public university for their politics, which it being a public institution, I think would actually provide those protections). Interestingly, in googling, I found a very informative thread on this board from 2004.
As far as Kaepernick, I would imagine that the owners are probably concerned about blow back if they discipline too much. What are they going to do if the fire him, and the next game, no one stands up for the Anthem, both in continuing his protest, and protesting his firing? I don’t know how likely it is, but it has to be something that weighed on their decision.
You may see that this weekend - Seattle Seahawks May Be Planning A National Anthem Protest For 9/11 - TPM – Talking Points Memo