You should read your link in greater detail. The NRLB recommended taking the employer to court in that case, but we'd have to see how that case plays out to kno

You should read your link in greater detail. The NRLB recommended taking the employer to court in that case, but we'd have to see how that case plays out to know whether firing employees for skipping work to attend a protest is not legal. The NRLB is quasi-judicial, their word is not law.