I spoke to an AFTRA representative on a set about this recently.
Apparently, if you are in any one of the acting unions, you're in the 4As, which is their parent union. (Associated Actors and Artistes of America.) Therefore, you're not supposed to take non-union work that falls under any of the unions' jurisdictions. That means if you're in AFTRA, you're not supposed to take non-SAG work OR non-Equity work.
I have a major problem with that... I don't understand why joining one union should give you the limitations of three unions. ESPECIALLY since two of those unions are closed unions. If I can't get into SAG or Equity, then why should I be prevented from working non-SAG or non-Equity? They shouldn't be able to have it both ways.
This is exactly why we need the unions to merge.
Anyway. From what I've learned, it seems doing non-union work under a different union jurisdiction is frowned upon, but there isn't much that they can do to stop it. So whether you do it or not is really just a question of your own union loyalty and personal morality.
I starred in a short film called
Magnetic Personality. Check it out!