There was an episode of the U.S. version of The Office where an exec said they'd all be fired if they got "even a whiff" of unionization. And really openly to dozens of people, not in any sort of wink-wink way.
I figured this was a legit threat in the U.S.
So not advocating that we use The Office (a sitcom) as a reference for American labor law, but I think Jan’s statements might be permissible. As long as her reasoning is that the increased cost of the workers being in a union will lead to the branch closing, not that the branch would be closed in retaliation, it would be fine.
Companies can and often do complain that if workers are in a union, the company’s operating costs will increase, which will consequently have adverse effects on the workers like layoffs, plant closings and so on.
To be clear, this is my understanding of legal issues in a sitcom. I am not necessarily advocating Jan’s point of view, our labor laws as they stand, or anything else.
"Due to increased costs (read: unions), we're reducing/eliminating employment."
"Due to decreased productivity (read: FMLA), we're reducing/eliminating employment."
I guess it works. I don't really understand this stuff.
"We don't think you fit in with our culture" - Legal.
I think this is why any crime where the intention is part of it is so hard to prove, like discrimination, hate crimes, etc.
As they say: The devil is in the details.
Firing the individuals who are trying to start the union - illegal.