Paul Kersey responds to the pro-union emailer in this post:

Jonah, about that pro-union email:
1. Your correspondent is right that rising labor costs create an incentive for the use of more capital, but that isn’t the only factor in play here, because unions affect more than just wages — work and seniority rules can make capital investments less valuable. I have a copy of the Ford/UAW contract in 1941 here; it’s 24 pages long. The 2007 agreement went on for 1200 pages. The notorious jobs bank that kept employees on the payroll for years while they weren’t working was in part a response to automation. Unions can subvert the use of new technology too and it can be in their interests (at least in the short term) to do so.
2. Comparisons to Europe are interesting, but there’s something of an apples-to-oranges factor here, you’re dealing with more extensive welfare systems and different labor laws. It’s worth noting that Ireland, which according to your correspondent had higher unionization rates in manufacturing and higher productivity growth between 1980 and 2005, also had a big drop in unionization, at least overall (I couldn’t find specific numbers for Irish manufacturing) from 1980 to 2003 — with union membership falling from a high of 57.1 percent of the workforce in 1980 to 35.3 in 2003. Rising productivity and falling union density — even if starting from a very high point — means that the role of unions in terms of boosting Irish productivity is at best unclear.
3. Getting back to the US, our research on right-to-work laws found that RTW states had lower per-unit labor costs, meaning that whatever capital improvements employers had in non-RTW states were not enough to overcome wage and benefit costs imposed by unions.
4. If you want to compare the performance of unionized versus non-unionized companies in the US, why limit yourself to Costco versus Wal Mart? Anyone want to talk about the auto industry?
5. Your union correspondent is right about one thing — there’s nothing in economic theory that says that unions have to be a drag on an economy. In my humble opinion unions the real problem is a clunky federal law (The National Labor Relations Act) that divides the workforce into rigid bargaining units and then says that either everyone in the unit is represented by a union or nobody is. I can’t think of any other situation in the US where a competent adult can have a representative chosen for him by others without some way to opt out as an individual and pick his own rep or negotiate for himself. The practical effect of the law has been to make unions largely unaccountable to the men and women they represent. If the lines of accountability were clearer, it would probably be easier for unions to win worker support on the merits and union officials wouldn’t need to push for things like card-check and binding arbitration. I don’t think that’s what we wanted as a society, and I don’t think union officials themselves realize just how out of whack the incentives they work under are. But that’s the law we have, and it’s a big part of the reason why unions in the US have the sort of negative effects, and poor reputation, that they do.