Taxes, of course. Yes, that dreaded word. I prefer letting the free market solve its problems usually, but as far as companies poeaching from others is concenrned, it would be in the national interest to ensure that companies feel comfortable to upgrade workers' skills without fear of poaching from other companies. Certainly it wouldn't be fair if one company is always upgrading its workers skills while another company poaches the workers with a small bonus. Obviously one company would be benefitting from the generosity of the other until finally the other could only go bankrupt under the unfair competition.

Alternatively, no company invests sufficienty for worker retraining, but then labour skills fall behind, and those companies in need of qualified workers start looking abroad. Not good for the US economy overall. While I like free markets, if we slavishly adhere to them even when it's clear that they're flawed, while more pragmatic countries are willing to experiment, then clearly companies will start moving there because of the security provided by ensuring that all companies invest in worker training, even if it is through personal income taxes taxes, with all of society contributing and benefitting from it, with no company fearing retraining its workers to ensure the economy works well.