I'm not a lawyer of course. Would they be able to find information during discovery? Either they can find a comparable store that wasn't shut down, that is all the factors that would matter to the business, or a document about why?
They might find something if it got to discovery, but you need a credible case to get there in the first place. Even if they found email saying "lets close the store because we don't want to work with unions" im not sure what that would be illegal.
Regarding the weak evidence, you brought up two other valid considerations.