From Letters of Note:

South Park: Bigger, Longer & Uncut is a feature length movie based on the animated series, South Park. Prior to its release in 1999, the movie’s creators – Matt Stone and Trey Parker – were asked repeatedly by the MPAA to alter the film in order for it to gain an R rating rather than an NC-17. Below is a memo sent by Stone to the MPAA, in response to such a request.