Nothing. But at that point it's an extra step of having to go into Steam and do that and how many pubs will go through that process of making up a fake title and company name? We all know who the active companies are and we can call them out for that in-game.
Voting could work too... I'm not opposed to that.
I don't necessarily agree with whoever brings the most people. For instance on the Union side last night Major Tyler only had 5 or so 9th New York guys which is much lower than the 9th normally has for that event. With that said I would vote for him even if my company had more guys as he needs that officer class and I would ask my guys to vote for him too because I fight with a musket and rifle I don't need that officer spot. Plus he'll often lead a larger group than just his guys including pubs who agree to follow.
Also please know I use Major Tyler as an example for the Union side. There are a handful of 'strong' leaders on the Union side I would do the same for.