The recent brain fart from president Trump has yet again distracted the public as to the real motivations of such snips of feigned disdain about respect for the country. And the belief that a employer can force employees not to voice their beliefs. Kneeling as a form of protest becomes an important freedom under attack.
While this seems like yet another simplistic Alt-Right solution, it falls within the GOP goals of legalizing corporations to require contributions to candidates by their employees. This has been floating around congress for years. With the Citizens United decision the push has been on to allow control of contributions, and in effect the political opinions of the corporate employees in violation of their democratic rights to voice their own political beliefs.
IF you can force employees to stand for that national anthem, then you can control their political contributions, and later whom they vote for.