I ran into this (on a very minor scale) while working at a grocery store part time during my early community college days. The store was unionized, but there were at least three different unions, depending on which department of the store you worked in. I ended up in the bakery working evenings, the only one manning the counter there, right across from the deli. There were times when I couldn't run to the restroom all evening because the three deli employees were in a different union and couldn't come over and watch the bakery counter for five minutes.