I read this on OFST recently, so you can skip to the punch if you remember it.
A union worker was on vacation in Reno and decided to visit an establishment that is illegal elsewhere. However, being a good union man he wanted to make sure he was - er - served by a fine worker-oriented establishment. Upon entering the first such he asked the madam if it was a union shop. She averred that it was not. He asked what the house cut was and she told him it was 80%. Finding this quite unsatisfactory he went elsewhere.
Unfortunately, each establishment he visited told a similar story. However, he kept looking and was finally rewarded by a madam who told him proudly that she did run a union shop. When asked, she told him the house cut was 20%. Finding this to his liking he said, “That’s all fine. Just fine. I’d like to spend some time with that young blonde lady at the bar.”
“An excellent choice,” she informed him. “Darla is a wonderful companion. But,” she indicated the septegenarian on the couch, “Edna has seniority.”