This article is from the Stand-up Comedy FAQ, by Steven Rosenthal and Steve Silberberg (firstname.lastname@example.org) with numerous contributions by others.
In order to appear in any major motion picture, you must have a Screen
Actors Guild (SAG) card. It's a catch-22 though. You can't appear on screen
until you get a card, and you can't get a card until you appear on screen.
Here's their number.
Screen Actors Guild