Luckily, unlawful termination doesn't require proof beyond reasonable doubt.
So if the employee was fired on the spot, that would pretty much guarantee a win in most states unless the boss could show that they had already planned to fire them before they shouted "unionize".
If the boss fired them a month later, that would be a different story. But yeah, the rest of that is valid.
You don't have to do anything, true. Feel free to completely disregard the Bible.
That being said, don't pick up Lord of the Rings, ignore it's genre and declare it pointless because Hobbits don't exist. The Bible has so many genres, because its a collection of stories and books rather than a single book, and you probably aren't aware of most of those genres because they no longer exist.
Again, feel free to completely ignore the Bible if you'd like, but saying that it's a mistake for anyone to try and figure out what one of the most influential books in the history of mankind was originally intended to say is wrong.