Ind. Code § 8-1-2-73

Sec. 73. In all trials, actions, and proceedings arising under the provisions of this chapter or growing out of the exercise of the authority and powers granted in this chapter to the commission, the burden of proof shall be upon the party adverse to such commission or seeking to set aside any determination, requirement, direction, or order of said commission to show that the determination, requirement, direction, or order of the commission complained of is unreasonable or unlawful, as the case may be.