I think a much better way to protect employees would be some form of enforced employee ownership. Stay somewhere for 3 - 5 years? Great! You get voting shares of stock and a voice in how the company is run.
We don't see this very much, but people don't really demand it either. If people started striking for ownership instead of salary and benefit increases, I'd bet that'd change.
I highly doubt that would be at all practical. You're basically suggesting that if you hire someone and they stay past a certain time, they will own part of your company forever. This removes the agency that owners have over their own businesses, and makes it so that no one would want to keep employees longer than 3-5 years (or whatever the threshold would be), resulting in guaranteed turnover.
It also gradually removes the barriers between workers and capital in a positively Jeffersonian way. Owners who weren't comfortable with that could, of course, fire people every 3-5 years, but firing and hiring isn't free either.
I've always thought that it might be an ideal solution to wage capitalism to force owners to sell equity to their employees at some predictable rate.
Pfft, there are so many restrictions on stock usage such as proxy agreements to the CEO, founder stock with 10x voting rights and so on that it might as well be useless for that.
We don't see this very much, but people don't really demand it either. If people started striking for ownership instead of salary and benefit increases, I'd bet that'd change.