OK, so whoever first coined the term "smoking gun" as a euphemism probably didn't have a few mildly suggestive e-mails in mind.
Regardless, that's what we have--three short documents that the International Association of Machinists and Aerospace Workers calls the "smoking gun" in the labor board's case against Boeing.
At issue is whether Boeing built a new 787 Dreamliner plant in South Carolina as a kind of retaliation against unionized workers. Such actions would be illegal, and that's exactly the reason that the National Labor Relations Board filed a complaint against Boeing.
The e-mails, which Boeing confirms as authentic, show executives weighing the pros and cons of building a Dreamliner plant in South Carolina and not Washington.
"Creat(ing) a non-union, competitive workforce" figures heavily into the pros section of reasons for the company to set up in South Carolina (as, no doubt, one would expect it to).
But whether this kind of decision making crosses over into being "retaliatory" will be up to a judge to decide.