Economists Support Move to Card-Check Union Certification in U.S.

The Wall Street Journal has a story reporting on a letter sent to Congress by three dozen economists, including two nobel prize winners, arguing in favour of the Employee Free Choice Act.  As we have noted several times here, that legislation would, among other things, allow unions to be certified by a card-check rather than a mandatory ballot.  Here’s the letter, with a list of signatories.
The economists share President Obama’s opinion that a health economy and strong America requires a strong middle class, which does not at all exist right now.  Building up the labor movement is seen as a way to stem the tide of the growing income disparity in the U.S., which many economists, political scientists, and labor experts argue is due in large part to many years of deregulation and weak labor laws.   The Journal story refers to one economist who argues that a 3 percent increase in unionization will lead to a 1 percent decline in employment.  She apparently based that opinion on a study of Canadian laws!  I’m not aware of that study, and given how often American scholars misinterpret Canadian labour laws and studies of it, I am suspicious of her description of it.  There are so many variables involved, I have doubts that the mere fact of unionization can be shown to cause unemployment?  For example, sometimes workers join unions because they fear downsizing is coming and they want some voice in the process.   When the downsizing then occurs, is it the result of unionization?  Of course not.  You would have to read the study carefully to see what was measured.
Any of you industrial relations scholars out there know what study she is referring to?