Do Indiana teachers have to pay union dues?

Membership is ISTA is voluntary.   In 2011 the Indiana State Teachers Union had 7% fewer members paying their dues  but revenue was increased enough to offset that.  The ISTA Exposed site is a source of information and their blog gives updates.

"Membership (in Indiana) is not mandatory.
Despite what may be said otherwise, membership in ISTA is voluntary. While signing up is subtle, it is not required as a condition of employment.
Members of ISTA sign this agreement which allows schools to deduct, via payroll, union dues and PAC contributions.
As pointed out on the Political Activity page of this website, this taxpayer-funded mechanism for collecting PAC contributions for the union reaps the vast majority of its receipts. By signing this form, school employees make it very difficult for themselves if and when they decide to resign from the union.
Indiana Professional Educators, Inc., an Indianapolis-based alternative teachers' professional organization, has produced a fact sheet on the requirements of resignation from ISTA.
ISTA also provides a Waiver of Membership form to be completed to not join their union in the first place. All a teacher has to do is fill in the local union name, fill in his or her name at the bottom and sign it.
The form must be signed in the presence of a union official, who acts as witness, so it's reasonable to assume a little intimidation will be thrown in."

Related: Wisconsin teachers choose not to pay union dues. ...