Romney's video (and presumably his next RtW salvo as well) is just plain wrong. The video features a New Hampshire business owner, one in the warm grandpa mode, talking plaintively about how his business is a family and he has "reasonable confidence" his workers are happy and he's just worried about them, the workers:

What if they don't want to join the union and the union says you have to join? What happens to them? Do they have to leave the company because it's a union house? Well, to me that's absolutely wrong. Absolutely wrong....We live in the Live Free or Die state and they can damn well choose whether they want to join an organization or not join an organization.

As it happens, it is absolutely wrong to say that workers have to leave a union employer if they don't want to be in the union. That is, it's a factually incorrect statement. A refresher on the facts, from the post I'm glad I wrote once so I wouldn't have to rewrite it every single time:

["Right to Work"] proponents would have you believe that without RtW laws in place, you can be forced to join a union in order to get a job…in a unionized workplace, a point they tend to gloss over. I mean, really, it would be nice if job=job in a unionized workplace, but that’s not remotely the case. In reality (PDF), though, you can never be forced to join a union—you can only be required to pay dues directly related to work the union does representing you.

So there is no circumstance (barring an unimaginably massive, pro-union overhaul of labor law) in which Romney's grandpa figure would have to worry that his anti-union employees would be driven from the warm family embrace of his business because of their refusal to join a union. What he really appears to be worried about is that his workers may unionize—buried in the video is an admission that what makes him want RtW is the concern that the NLRB might make it easier to unionize.

All his talk about the union as a third party coming between him and his warm loving family of employees, then, is a cover for the fact that he's concerned that those very employees, the ones he's "reasonably confident" are happy, might want to join a union. After all, a currently non-union workplace is not going to become a union workplace without support from a majority of the workers. But by weakening unions in a state, RtW makes it less likely a strong union will be available for workers in that state to join should they wish to. RtW prevents employers and unions from agreeing to a "union security" clause, which:

...says that if the union represents you, you have to pay your share of the costs they incur. So what banning that type of agreement means is that if someone gets a job in a unionized workplace, the union has to represent them, but they have no responsibility to the union. They get the wages and benefits negotiated, however improved those may be (union members earn, on average, 28% more than non-members), and don’t contribute to the costs of negotiating. If they’re fired illegally, the union represents them for free, no matter how much staff time and resources go into defending them. And if they feel like the union didn’t do well enough representing them for free, they can sue. You can see where that goes. People enter as freeloaders, happy to have improved wages and benefits and help when they have a problem with the boss, and happy to let someone else pay for it. But that freeloading weakens the union, and in the end, working conditions and pay are driven down for everyone[.]

That's the reality of what Mitt Romney is pushing today, however much grandfatherly rhetoric about management and workers as one big happy family he wraps it in.

