Grammy performers keep their buttocks, nipples and genitals under wraps.CBS

American broadcaster CBS has issued a warning against wardrobe “obscenity” ahead of its airing of the Grammy Awards on Sunday. The warning, which came in the form of an email headed “Standard And Practice Wardrobe Advisory”, was published on Deadline.com. The advisory made clear that buttocks and “female breasts” - specifically the bare sides or “under curvature” - should be adequately covered, and made an intriguing reference to “puffy” bare skin that accompanies exposure of the genital region.

Obscenity or partially seen obscenity on wardrobe is unacceptable for broadcast," the note added.

The warning follows a lengthy court battle over indecency and obscenity standards on U.S. network television.

In 2010, singer Pink performed upside down in a flesh-colored bodysuit, while Rihanna last year wore a plunging black dress on the red carpet.

Performers at Sunday's three-hour show in Los Angeles include Rihanna, Justin Timberlake, Maroon 5, Frank Ocean, Alicia Keys and Elton John.