How can I write a letter to ask for permission to watch an R-rated film for a club?

I am in charge of getting permission to watch an r-rated film for our high school's film club. There are a few sex scenes and slight nudity. But it is a foreign film so its not anything distasteful. I am not sure how to phrase this in the letter or how to address it (to whom it concerns? dear parents?), If anyone can give me a clear format that would be lovely. Thanks!