The two largest teachers' unions in Michigan have lost one-fifth of their membership since 2012, according to Michigan Capitol Confidential. Michigan Gov. Rick Snyder, a Republican, signed right to work into law in 2012.

The Michigan Education Association has lost more than 23,000 dues-paying members since 2012. In the same time frame, the relatively smaller American Federation of Teachers-Michigan lost more than 4,800 members.

The damage to unions might be even worse, were it not for union security agreements made with local school boards. The agreements keep members from opting out of their union until collective bargaining agreements expire. Until a recent court ruling, the unions also made it very difficult for other members to opt out — before September, they had to mail their resignation to a hard-to-find address during one month out of the year.

In addition to right to work, Tom Gantert with Michigan Capitol Confidential cited privatization of non-instructional services for the membership decline. The number of public school students in Michigan is also falling. And public charter schools, which are typically non-unionized, are on the rise in Michigan.

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