The pimps' union is called the "Mecs (Guys or Blokes) Paris Protective Association" (MPPA), which also stands for "Motion Picture Producers Association", an organization which had given Director Billy Wilder some trouble.
According to an article in the 21 October 1962 edition of the New York Times, the sprawling Rue Casanova set took three months to build at a cost of $250,000 ($2.45M in 2022), and included 48 buildings and three converging streets.
Shirley MacLaine was not happy with the script, and thought even less of the film after it was finished, calling it "crude and clumsy". She was surprised to get a Best Actress Oscar nomination out of it, saying, "I would have been nonplussed had I won it."
In order to be able to play Irma properly, Shirley MacLaine traveled to Paris to see what it was like for real Parisian prostitutes. They were eager to tell her what it was like, and very willing to answer any questions she had. When asked if she would like to "watch them in action", she politely declined, but to her surprise they became indignant. They requested that she watch one of their weekly customers with three of the girls through a small window in the hotel door; she unwillingly obliged.