Wage theft is the most common crime in the US, is estimated to occur to ~20% of all employees and equal tens of billions a year, and no one talks about it.
How many union members do you think experience wage theft?
The US Department of Labor takes wage theft very seriously. If you report it to them, at no cost to yourself, they will investigate it and almost certainly scare your boss shitless so he'll never try it again.
Probably they could do a better job of advertising this to workers. Many workers experiencing wage theft probably are not aware of their options, and that's a problem. But when used, it works. I've seen it work.
If they take it so seriously, why is it so underused? I don't think this is a lack of information; people who are highly precarious can't take these kinds of risks, even if they're just percevied.
There are all kinds of de jure considerations that purport to protect workers, but they fail without an organization by and for workers to actually ensure they're enforced.
The first real job I had was the first time I saw the efficacy of the Department of Labor. I was working at a bean processing plant; semi trucks with trailers full of fresh green beans from the fields dropped beans off at the plant where they were cleaned (my job was to pick out the bits of small animals the harvesters chewed up), chopped, cooled, and loaded onto another truck. The entire operation hinges on the trucks arriving just in time.
Well sometimes a truck is late, that's just the way the world works. In one of those cases, my boss asked us to stay at the plant an hour late; the truck driver was on the phone and said he'd be there shortly, but we had nothing to do but sit around on our asses twiddling our thumbs. One of my coworkers, more experienced than me, asked if we'd get paid while waiting. My account of the conversation that followed:
Boss: "Well uh, we're all just sitting here doing nothing so.."
Coworker: "The Deparment of Labor says..."
Boss: "WHOA WHOA WHOA! I was just kidding of course you'll get paid!"
Immediate backtrack. He turned on a dime as soon as he realized there were workers who knew their rights. I think information is the key. There is no substitute for workers knowing their rights.
Probably they could do a better job of advertising this to workers. Many workers experiencing wage theft probably are not aware of their options, and that's a problem. But when used, it works. I've seen it work.