A prank letter ordering students to attend a "mandatory vagina inspection" in the gym of a Minnesota high school has administrators -- and police -- looking for who's behind it.

The letter (see below), written on official-looking letterhead for Prior Lake High School in Savage, Minnesota, was hand-delivered to the mailboxes of at least 50 families, the Minneapolis Star-Tribune reported.

The note warns female students to remove piercings before the examination and threatens to keep them from graduating if they don't "pass."

The stunt generated lots of social media chatter, in which some posited that the letter was a "senior prank" gone wrong.

While some Prior Lake students said in an interview with local news outlet KSTP (see above) that they found the prank funny, Savage resident Douglas Devries said, "It was very graphic and very inappropriate."

School district representative Kristi Mussman told the Star-Tribune the joke was “done in extremely poor taste." Savage police are now investigating, KSTP reported.

Here's what the letter looked like: