Source? This seems like a pretty clear-cut lawsuit waiting to happen. I'm aware that not everyone can afford to take on legal action, but I'm skeptical that it's widespread.
"From this article, The Department of Labor’s wage and hour division estimated that nearly 84 percent of full-service restaurants it investigated between 2010 and 2012 had violated labor standards, including but not limited to tip violations."
There isn't really anything like a clear-cut lawsuit when you don't have the money to retain a lawyer, and when the award youd get from winning isnt enough to entice a lawyer to take your case on contingency