Tax lawyer Dan Evans writes, Taxing Political Expenditures:

The Supreme Court's recent decision in Citizens United v. Federal Election Commission severely restricts the ability of Congress to regulate, much less prohibit, the use of corporate money to influence elections, but what about Congress's power to tax that money?

As it is now, corporations cannot claim expenses of attempting to influence elections or legislation as business expense (see § 162(e)).  So corporate profits that are spent on electioneering are effectively subject to income tax at the corporate level.  The shareholders bear the burden of the tax, but very indirectly.

But what if the expenses of electioneering were considered a form of a dividend? … [I]t would not be unreasonable for Congress to say that, if a corporation uses its money to advance the personal political beliefs of the officers or shareholders, that money should be considered to be payments to those officers or shareholders.  For most publicly-traded corporations, dividends are not tax-deductible by the corporation, so income paid out as dividends is taxed twice, once at the corporate level and again at the shareholder level.

But the really nasty part is that Congress could offer corporations a choice:  If the political expenses are approved by the shareholders, then the expenses could be considered a dividend to those shareholders, but if the political expenses are approved only by the board of directors, then the income falls on the directors alone. … Taxing directors or shareholders on the money spent on corporate electioneering might not solve the problem of corporate influence, but it might make it more difficult and more painful.