The actress told Deadline Saturday that she was bowing out of her Amazon flick, "G20," for now -- saying ... "I love this movie, but I do not feel that it would be appropriate for this production to move forward during the strike."

She adds, "I appreciate that the producers on the project agree with this decision. JuVee Productions and I stand in solidarity with actors, SAG/AFTRA and the WGA."

It's a bold move, and speaks volumes on where Viola's priorities are. Like we said, just the other day ... the producers behind "G20" got the green light to go ahead and continue with production -- even though Amazon is obviously a major studio. The fact an independent production company, MRC, is also behind it appears to be the reason it got a pass.

In any case, it would seem moving forward while thousands of other actors are on the picket lines wasn't sitting well with her ... which is interesting, because a lot of other big stars are also attached to independent flicks right now that got SAG waivers as well.

Those names include ... Anne Hathaway, Jenna Ortega, Paul Rudd, Matthew McConaughey, Mark Wahlberg, Sigourney Weaver, Mads Mikkelsen, Ben Kingsley, Dave Bautista, Ice Cube, Dakota Fanning, John Malkovich, Sean Bean, Rebel Wilson ... to name a few.

Again, them being attached to indie films -- with no direct ties to AMPTP -- is why they can keep trucking (especially overseas) ... but some have raised an eyebrow regardless -- viewing their continued work as a betrayal. That's, perhaps, unfair, but it's a real POV out there.

Now that Viola is putting her foot down ... it may be a signal for other mega stars to do the same -- even though they can technically proceed through the SAG indie loophole.

The principle of the matter could be why Brad Pitt reportedly stood down on filming as well. There was word that his F1 movie, "Apex," was continuing to film in Hungary last week -- with some claiming BP himself even got behind the wheel at one point for some scenes.