Versions of this story can be found all over the internet. The authors are unknown. One version can be found by Madeleine L’Engle in “Bred any Good Rooks Lately?”
In a certain city in Eastern Spain, there was a movie theater. The builders of the theater only built a single emergency exit door, rather than the two required by law. Sure enough there was a fire and several people were trampled to death. The moral: Don’t put all your Basques in one exit.