The transparency laws aren't the cause of the discontent. The cause is the fact that current employees are underpaid compared to new recruits. Businesses are just upset that they can't shaft their workers.
It is a little bit of both, but the discontent is because workers find out exactly how much businesses are able to shaft their workers. I know I was upset when I found out a new hire got more than me after years of service. Boy did I learn a valuable lesson back then.
Well, "US pay transparency laws result in worker discontent," is just not what one should imply from a causal stand point.
"US pay transparency laws result in workers realizing that their employers are trying to underpay them and this results in workers being discontent," is the truth. This is the whole point of transparency, which I assume is what you are getting at. The transparency doesn't share any of the blame however, so the wording of the title is unfair.
People are always unhappy. My wife is an exec and most of her direct hires are clueless as to their worth. One of her direct reports got a promotion and when another found out, he complained. Meanwhile, he did less than half the work of the other. When she pointed that out, he got quiet. He’s probably still going to quit because most people can’t take the truth.