The debate has America split—literally. With Wisconsin's adoption of so-called right-to-work legislation earlier this year, 25 states now prohibit mandatory union dues, and with legislation being pushed in several more states, the right-to-work movement is talking about a national "tipping point." Under right-to-work legislation, no person can be compelled, as a condition of employment, to join or not to join a labor union or pay dues. Republican legislators in Missouri passed a right-to-work measure this month, but Democratic Gov. Jay Nixon has said he will veto the bill. A bill almost passed in New Mexico, and backers are pushing similar...