Wal-Mart closes stores when unionization gains momentum. Pizza Hut (hearsay) has an undocumented policy of "fire people who talk about unions." When you're pulling near minimum wage, losing your job over labor laws isn't very appealing. I believe Chick-fil-A put wage discussions as fireable in my paperwork, as have other tech companies.

Some of the people who need unions the most can't get them, as the Labor Board hasn't enough teeth and the public isn't very favorable toward unions.