Ohio Rev. Code § 124.63: Taxpayer's suit.

The right of any taxpayer to bring an action to restrain the payment of compensation to any person appointed to or holding any office or place of employment in violation of sections 124.01 to 124.64 of the Revised Code, shall not be limited or denied by reason of the fact that said office or place of employment has been classified as, or determined to be classified as, not subject to competitive examination; provided any judgment or injunction granted or made in any such action shall be prospective only, and shall not affect payments already made or due to such persons by the proper disbursing officers, in accordance with the civil service rules in force at the times of such payments.