In the long term, unions (and pro-society policies in general) benefit the employer by ensuring a cybernetically stable supply of labor.

Most employers obviously aren't thinking that far ahead, though. They would rather cut corners (import cheap labor), and then be surprised when there are systemic failures in their labor supply.

We're gradually seeing that hit in America as the global USD goes under, the well-endowed Boomers retire, and USA is a less appealing immigration destination.