Michigan has become the 24^th “right-to-work” state in the union, making it the most heavily unionized state—by far—to enact such a law. Before now, that honor had belonged to Nevada, the 14^th most densely unionized state in the union. Michigan ranks third.

Michigan had more than 670,000 union members in 2011, according to our compilation of Census figures. That’s more union members than there were in Nevada and the next five right-to-work states on the most-unionized list—Iowa, Alabama, Nebraska, Kansas, and Wyoming—combined.

The consequences of introducing such a law—which prohibits unions from making union membership or dues payments mandatory—to such a labor-rich state have been debated furiously since the bill was introduced earlier this month. But definitive data on the effect of right-to-work laws on the health of unions have been elusive.

I can see why. I’ve crunched some numbers on states’ union strengths over the past 10 years, and it’s hard to pick up on any trends among the two groups of states, let alone isolate right-to-work as the determining factor in those trends. For example, it is true that 19 of the 20 least-unionized states are right-to-work states. But is that because of the impact of the right-to-work laws? Or did right-to-work laws pass so easily there because of a relatively weak union presence?

Still, the 10-year check does merit a closer look, because it was in 2001 that Oklahoma became a right-to-work state. This raises a topic for study: How did Oklahoma’s union situation change after a decade of right-to-work?

In relation to other states, at least, there wasn’t much that changed. Oklahoma’s union density rate—the percentage of wage-earners who are union members—fell from 8.4 percent in 2001 to 6.4 percent in 2011. But fourteen states reported a steeper drop than that over the past decade, while 23 reported an equal or smaller decline. Twelve states actually reported gains in union density (only two of which were longtime right-to-work states). All told, compared with other states, Oklahoma had the 30^th-highest density rate in 2001, and the 30^th-highest rate 10 years later. 

In terms of overall union members, Oklahoma had some 93,500 in 2011, down from 115,900 in 2001. Over the same period of time, 14 other states saw a net gain in union membership—including five longtime right-to-work states. But 36 states saw decreases in union members, and among those, Oklahoma’s 19.3 percent drop landed it roughly in—you guessed it— the middle of the pack.

The biggest loser? Only one state lost more than 300,000 union members over the past decade: Michigan.