I know of SAG actors who take the occasional non-Union gig, confident in the assumption they will not get caught. After all, the Guild does not police every production, turning over every rock looking for members who are breaking the rules, and there are plenty of unscrupulous producers who are willing to turn a blind eye for the right actor and claim ignorance if a SAG rep shows up on their set. However, if a member in good standing got caught, he/she would have broken SAG-AFTRA’s only unbreakable commandment, Global Rule One: “Never Take Non-Union Work”. Specifically:
“No member shall render any services or make an agreement to perform services for any employer who has not executed a basic minimum agreement with the Union, which is in full force and effect, in any jurisdiction in which there is a SAG-AFTRA national collective bargaining agreement in place. This provision applies worldwide.”
The penalty would be a heavy fine to the actor or possibly expulsion from the union and the producer could be barred from contracting with SAG-AFTRA in the future.
If I am hired on a non-Union project as a Fi-Core actor, do I have to show proof of my status?
You do not have to show proof of your Fi-Core status. You will not be given a special card or anything like that by the Union. If you represent yourself as FC on your resume, the producers who hire you will, in all likelihood, simply take you at your word. If they chose to do their due diligence, I'm sure they could call SAG-AFTRA to ask if you are a member in good standing. most of the time however, the assumption is, with all the drawbacks associated with FC status, you wouldn't put it on your resume if it weren't true.
Kenzo on IMDb