I don't know if they have or not, but I do know such things happen. I worked in restaurants in San Diego back in the 70's, and the wait staff didn't cotton to folks who stiffed them or left less than what they expected. By the way, as a bus boy, I was to be given a percentage of waitresses' tips, and there were several who'd come up with the flimsiest of excuses to give me less than my cut. "Oh, you didn't do this. You were too slow doing that, so I'm going to have to give you less today..." They, as it turns out, were the ones who *****ed and moaned the most when someone left little or nothing.