No Trace

[A.J. Jones, Starbucks' executive vice president of communications] also claims that the union's stipulation of wanting to observe proceedings violates the National Labor Relations Act, which prohibits the recording of bargaining sessions.

The union has refuted this claim, saying that it wants union members to sit in on the [Zoom] call, not record it.
Why are Starbucks workers striking?

And how would the Starbucks Workers Union propose that members be prohibited from recording the proceedings? There are any number of ways to make a video of what's happening on a computer screen. Sure, the Union could expel anyone who released a recording, but that's closing the barn door after the horse has gone off and founded a cryptocurrency start up. For the Union to claim that members observing the call would be stopped from recording it is either hopelessly naive or openly disingenuous. Just because someone lacks access to the Record function built into Zoom does not mean that they have no ability to make a viable recording of the call.

While I understand that unions are meant to advocate for their members, the assumption that all approximately 7,000 people in the Starbucks Workers Union are either too ethical, or too tech-illiterate, to figure out a way to record a Zoom call without anyone knowing that they've done so goes beyond simple advocacy. It's possible that the Union's leadership are themselves lacking in the sort of technological savvy that would give them an understanding of how a call might be recorded, so, for the sake of argument, let's give them the benefit of that doubt. In that case, why not ask Starbucks why they determined that members observing the call carries a risk? (Personally, I suspect that Starbucks hasn't granted the Union the benefit of the doubt, and I'm not at all surprised by that...)

The adversarial nature of the relationship between the people who work for companies and the people who own and manage them is tailor-made for this sort of thing. The Union has no incentive to believe that it would be trivially easy for any participant or observer on a Zoom call to record it, and Starbucks management has no incentive to believe that the leadership of the Union is dealing in good faith. And once neither side has an incentive to see the other as being an honest partner, things quickly fall apart.