Indiana Code Title 20. Education § 20-29-5-2

Sec. 2. (a) A school employer may recognize as the exclusive representative of the school employer's employees within an appropriate unit a school employee organization that presents to the employer evidence of the school employee organization's representation of a majority of the school employees within the unit, unless:

(b) Before recognizing an exclusive representative under this section, the school employer shall post a written public notice of the school employer's intention to recognize the school employee organization as exclusive representative of the school employees within the unit.  The notice must be posted, for thirty (30) calendar days immediately preceding recognition, in each of the buildings where the school employees in any unit principally work.