Eclectablog lays out what Michigan Republicans are going for here:
Understand this very simple fact: the push to eliminate exclusivity and return to “collective bargaining pluralism” is nothing more than an attempt to weaken unions even further. It is being done for the exact same reasons the powerful automakers in the 1930s pushed so hard for it: it puts management, a unified group, in a position of power while unions and workers fight amongst themselves for the scraps they are tossed. Pitting members of your opposition against each other is a classic technique in warfare of any sort. It should come as no surprise to anyone that conservative groups and Michigan Republicans are using it to defeat labor unions and take away their power.In other words, this is a logical next step from the people who took advantage of a lame-duck session to ram through a freeloader bill and revive a law that had been repealed by a popular vote, then slashed funding for schools that signed union contracts delaying implementation of the freeloader law.