If the companies are backstopped by the govt prohibiting a strike, they will go down to the absolute lowest level tolerable, until people retire and nobody is willing to take on that job. Likely, we'd see what happens in other industries that create a bimodal tiered system, where the grandfathered employees are still paid well while the newer tier are paid a fraction. Or, wages will stagnate until the equivalent occurs.
Again, taxing the companies will make sure incentives are more aligned between workers, shareholders, and the public. The problem with one-sided approaches is that it's very easy to levy a fine that someone else has to pay. The public and the shareholders can favor an ever-rising tax as long as long only the employees are burdened with it. Taxing the company will ensure that everyone is incentivized to find a reasonable taxation level.
Theorize the govt owns land that has the sole unobtanium mine that the fulfills some public necessity. I have the only equipment that can process the ore. You have the only skillset to operate it. Overtime, my contract terms get to a point that you feel is unreasonable. But the govt says you can't walk away because the public needs their unobtanium. Your solution is that the government tax you for the privilege to continue to mine - which they've also said you can't walk away from. Meanwhile, I pay no penalty to continue to press you for less favorable contract terms so that I can make ever increasing profits. Does that sound like a reasonable arrangement or is it marching towards a Ones Who Walk Away from Omelas scenario?
By taxing me instead, it forces me to find the right level of salary to you, rates to the public, and profits for myself. Everybody has skin in the game, unlike when your scenario that gives you an ultimatum you can't walk away from.