It's All About The Money. That's All It's Ever Been About.

Some teachers hang onto the fiction that their local/state/national teachers unions exist to make their lives better, or perhaps to make the world a better (read: liberal) place.  They can choose to hang onto that belief with religious fervor, pretending that it's so, but we all know it's crap:

The president of Michigan’s largest union is instructing officials to prepare to sue its own members, according to a leaked memo issued after the state adopted right-to-work laws in December.

Steven Cook, president of the Michigan Education Association, circulated an email to local unions officials and staff instructing them to monitor revenue streams in light of the right-to-work laws, which are set to go into effect on March 27, 2013. The law allows workers to opt out of union membership unless they have an existing contract with their employer.

“We will use any legal means at our disposal to collect the dues owed under signed membership forms from any members who withhold dues prior to terminating their membership in August,” Cook wrote.
The tone of the message shocked labor reform activists.

“The level to which the MEA appears to be willing to go after its own members—the same ones whose interest they claim to represent—is amazing,” said Mike Van Beek, director of education policy at the Mackinac Center. “When it comes to their revenue, we know where their priorities stand.”

When you have to compel someone to give you money, there's a good chance your reasons for doing so are illegitimate.