When someone makes a payment of tax and they are under no legal obligation to do so, that person has made a voluntary payment that is generally nonrefundable.
An example of this is if a shareholder of a corporation attempted to file a refund for tax paid by the corporation, the shareholder would be denied that right for the refund.
Wrongful Voluntary Overpayment of Tax
There have been cases however when a taxpayer sued for a refund in regard to corporate taxes that were paid by the taxpayer for an erroneous claim that the taxpayer was led to believe he was personally liable for. This is situation, the taxpayer would have the right to file a claim for refund because he was in fact not liable for the corporate tax paid.