In order to deter aggressive tax planning, the Australian government mandated public disclosure of three line items from large corporations' tax returns. However, there is no evidence that the mandated disclosure led public firms to pay more taxes (Hoopes, Robinson, and Slemrod 2018). Instead, I find that firms strategically offset expected reputational costs by voluntarily issuing supplemental information. Specifically, when managers expect new reputational costs from the mandated tax return disclosure (wherein the disclosure reveals an unexpectedly low tax liability) and low proprietary costs from a supplemental voluntary disclosure (wherein the firm discloses its nonaggressive tax planning), firms are likely to voluntarily disclose information that both preempts and supplements the government's mandatory disclosure. Thus, when mandatory disclosures are incomplete, firms will voluntarily issue additional information to remain in control of their disclosure environments.